Scheme-it supports a list of primitive custom symbol types that allow you to create your own custom symbols. To place a custom symbol primitive into your drawing, click on the "Custom Symbol" category in the left sidebar and drag in the desired primitive. Custom primitives include Part Body and Pin.
The Part Body primitive is used as the basis for creating a basic symbol body. Shapes include rectangle, rounded rectangle, and triangle. When a Part Body primitive is placed in your drawing it is added to the project BOM.
Pin primitives allow you to drag in generic port pins for use in creating custom symbols. Port pins include top, left, bottom, and right positioned pins. Port pins contains wire nodes that allow you to connect them to other symbol pins.
You must drag a pin onto an existing part body. When you do so, the pin is placed on the side of the part body designated by the type of pin. The drop location determines the vertical or horizontal position of the pin on the symbol.
Pins may be moved along the symbol side they are placed on. Pins may not be moved do a different side of the symbol. To move a pin, delete the pin and add a new one on the desired side.