The ProMIDI interface is a doddle to fit - you plug the interface into your Amiga, you plug your instrument into the interface. Very little can go wrong here, although even so the manual includes a handy chapter on connections that you should read if you are in any doubt at all about what plugs into what. There's really only one support question concerning ProMIDI that we are asked now and again:

I didn't get any software with my ProMIDI that enables me to compose, play and save MIDI songs.

That's right, you didn't! ProMIDI is simply a hardware interface, not a software application. To compose, play and save MIDI songs you will need to purchase third-party software like (for example) Bars & Pipes.