To add a component from a library to an assembly:
Using the component thumbnail images:
The component is positioned on the cursor using the default attachment.
To change the attachment, hold down Ctrl to flip the component orientation, or press the up and down arrow keys to cycle through other attachments.
Using the context menu:
Move the cursor to the required position and left-click. You can add multiple instances of the same component. When you have added all required components, click on the Quick Access toolbar.