Hello. How do I make Pd to communicate with Ableton. For example I would like to trigger a bang in my Pd patch using audio or MIDI from Ableton to play or modify visuals. Thanks

you need a third party application which acts as a MIDI patch bay. I use loopMIDI (which is free and simple to use) for communicating from pd to ableton. I should imagine it would work the opposite way just fine. Then... it would be either a [notein] object (for midi notes) or a [ctlin] object (for CC values) which you would need to open in pd. If you are sending to a bang you would want [notein] but you would also want a [stripnote] object after the [notein] which removes the note-off value (without this you would get two bangs every time).

Important: make sure you open loopMIDI or whatever MIDI patch application you choose to use before you open Ableton and PD. Think of it like a hardware MIDI interface. If you open your DAW and then open the device it won't show up in the MIDI settings menu. It needs to be the first thing open.