Logic

1. Click the + icon in the top left corner of the track list
2. Make sure Software Instrument is selected in the pop-up window and make sure the Open Library option is deactivated and then click Create.
3. Click the Instrument slot for the channel you just created and select the path AU Instruments -> XLN Audio and select your plug-in.

Watch the video below for a visual guide:

If you are experiencing issues with finding your plug-ins in Logic, then please have a look at this article:

Plug-ins not showing up in Logic pro-x