Your thread title is quite clear and succinct and is what attracted me to this question. What you need to do is use the search tool on this forum, using broad keywords you think are relevant: triggering, live input, guitar input, audio for example. This question has been asked, and answered, numerous times before.
Secondly, you should be a little more specific about these ‘processes’ you wish to trigger. Max will allow an almost limitless variety of processes, involving digital audio, midi and video.
Digital audio chord recognition is very complex (MIDI chords are easy); better to use single pitches, and you should search maxobjects.com (and this forum) for the [fiddle~] object; sod it, here it is: