Find a sausage you like and start there. Maybe a fresh breakfast sausage, something that doesn't use cure. The collagen casings can be difficult, but buy a good quality one and you should be fine. You will learn by overstuffing a couple and having blowouts.
I watched quite a few videos on linking and stuffing sausage. Start there. Eric from 2 guys and a cooler is a good start, same and Duncan Henry. Very informative and easy to follow.
And please, reach out if you think I can help. That goes for anyone here on the forum.