Note: Whilst the MIDI In function allows for Trigger 2 to read incoming MIDI Data and play Trigger samples, SSD5 is a better-suited plugin for this sort of application. Users can download the Free version here. https://ssd5-free.dl.drumclassroom.net/
For more information on the difference between Trigger 2 and SSD5, refer to this article.
1. Insert a MIDI Track in Ableton (⇧⌘T, ⇧ Ctrl T). With your MIDI track selected, locate Trigger 2 in your browser, and double click to insert it on the track. ( Show/Hide Browser: ⌘⌥ B, Ctrl Alt B).
2. open the Trigger plugin by locating your device view (⇧ Tab), and clicking the wrench icon.
3. Go to the settings page in Trigger 2, and check MIDI in, set the channel and note according to preference.
4. In Browser, load up an instrument, make sure audition is set to "on". Make sure your instrument track is set to record arm. Click on one of the instrument slots, and ensure the instrument plays.
5. Insert a midi clip by highlighting an area in the track display, then right-click and press "Insert MIDI Clip" (Ctrl ⇧ M, ⇧⌘M). Double-click on the clip to bring up the MIDI note editor. Here, you will be able program MIDI patterns to use with Trigger, using the note that you select in your Trigger Settings page in step 3.