Apple Logic Pro X - Manual (Page 498)

Chapter 16 Mix a project 498
Add an audio effect plug-in
Do one of the following:
m Click an Audio Effect slot, then choose a plug-in from the pop-up menu.
The last visible empty Audio Effect slot in a channel strip is shown at half its height; use it in the
same way.
m Option-click an Audio Effect slot.
You can now choose legacy plug-ins from the pop-up menu.
Add an instrument plug-in
Do one of the following:
m Click the Instrument slot, then choose a plug-in from the pop-up menu.