Capturing Your Design Idea as a Schematic
The process sounds simple enough: place some components and wire them up - however, the challenge is in the details. On one hand there is the detail around the idea - will that complex concept actually work? On the other hand, there is the detail that comes with drafting a circuit that can have tens to hundreds of components connected by hundreds to thousands of nets - is it wired correctly?
For both of these reasons, an electronics design tends to evolve. The circuit will typically be created in sections: the processor and memory, the analog to digital processing of inputs, the display interface, the power supply, and so on. Altium Designer has a number of features to help you design in this way. You can capture the sections on separate schematic sheets then build up the overall design as you are ready. You can transfer a section of the design to the PCB editor then transfer additional sections when they are ready. You can even easily re-use an existing circuit, either using a simple copy/paste/reannotate process or as a device sheet where the source schematic is not edited.
Finding and Placing the Components
The heart of any electronics design is the components. And while you can of course create your own components, Altium Designer provides a powerful Manufacturer Part Search panel that can be used to search for real-world manufactured parts. If you have a managed content server, you can acquire those parts into that server. Acquisition involves creating a new managed component - using the Component Editor in its Single Component Editing mode - and releasing to your server.
The component that you ultimately solder onto the board needs to be represented, or modeled, in each design domain as a symbol on the schematic, as a SPICE model in the simulator, as a footprint on the board, and as a 3D STEP model in the file you hand off to the mechanical designer.
Read more about Building & Maintaining Your Components and Libraries.
Altium Designer's Components panel provides a powerful interface with which you can use to interact with all your components - both managed (server-based) and library (file-based). Additionally, for your managed components, the panel provides a filter-based parametric (faceted) search capability for specifying target component parameters. In addition, the panel also offers options to edit a managed component through the Component Editor (in its Single Component Editing mode), view the component in its source server, and perform component management functions such as component creation and cloning, or editing the selected component's Part Choices and Type.
Read more about Finding, Placing and Updating Components and Footprints.
Connecting the Components
Components are connected by wiring the pins together or by placing net identifiers to connect the pins in that net.
Read more about Creating Connectivity.
If the design includes high pin-count components, it is not practical to create all of the connectivity using individual wires. Multiple nets can be bundled into a Bus if they are members of a numerically incrementing set, such as Data0, Data1, etc. Alternatively, any combination of nets and buses can be bundled into a Signal Harness, which offers a visually and logically neat way of transferring multiple nets throughout your design.
Read more about Bundling multiple nets.
Spreading the Design Over Multiple Sheets
Small format printers are the norm today, so anything other than the simplest design will be spread over multiple schematic sheets. There are two approaches to organizing a design over multiple sheets: flat or hierarchical.
In a flat design, think of the design as a large, single sheet that has been cut into smaller sheets.
Alternatively, you can arrange the design in a tree-like, or hierarchical structure, using a symbol to represent each lower-level sheet.
Both approaches are valid; each has its own strengths and weaknesses. A flat design will be quicker to create but harder for others to follow signals and interpret the functionality, especially from a printed copy. A hierarchical design will take longer to draw as there are more steps to create the connectivity with the reward being a design for which others more easily interpret its functionality and follow the signals across the sheets. Hierarchical design is also important for design reuse and an essential part of a multi-channel design.
Read more about Multi-Sheet Design.
Compiling and Verifying the Design
The schematic editor is actually an intelligent drawing tool rather than a wiring tool. The connectivity defined by the wiring you place is established when the project is compiled. This approach of separating the capture process from the design analysis and verification process means you can place and wire quickly and efficiently.
Compiling the design builds the Unified Data Model - this single data model resolves many of the problems that come with the siloed approach of separate design editors used by other design environments. In Altium Designer, the compiled view of the design is available to all of the editors providing that editor with a complete view of the design.
Your designs are dynamically compiled and the Unified Data Model is available from the moment a project is opened - a true Dynamic Data Model. This 'dynamic compilation' provides speed of compilation and a constant listings of nets and components in the Navigator panel. It also makes it easy to work with circuits, rules and components in the schematic editor.
The design connectivity model is incrementally updated after each operation. This means that project compilation is not necessary to see the contents of the Navigator panel, run the BOM, or perform ECO.
Read more about Compiling and Verifying the Design.
Place a compile mask to hide sections of the design that are not ready for error checking or transfer to the PCB editor. When you are ready, click the control to collapse the mask, exposing the circuit to be included in the compilation process and design transfer.
Compile masks belongs to a class of objects called design directives. Use these to add design-level instructions (directions) to the schematic, such as: membership of a net class, identifying a location where the compiler is to ignore a specific violation, identifying a group of nets that are differential pairs, etc.
Hover over the image for a demonstration of a compile mask. 
Adding Detail to the Design
The output from the capture stage is an electrically complete and accurate schematic and a detailed and functional set of print-ready schematic pages.
When you are designing in the schematic editor, use templates to create consistent-looking schematics, enhance their functionality and readability with notes and images, and generate PDF output complete with bookmarks and additional component data.
Read more about Finalizing the Schematic.
Where to Next?
Like all of Altium Designer's design technologies, the schematic editor is designed to be quick to learn and easy to work in. Context sensitive right-click menus are used extensively and context-sensitive help (F1) and in-command shortcut lists (Shift+F1) are available everywhere.
If you are new to Altium Designer's design software, you might want to start with the concept to completion tutorial. Based around a simple nine component circuit, you will start with a blank schematic sheet and end up with the PCB along with the files needed to fabricate the board.
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