First thing you need to do is season the smoker. Check YouTube for a how to. It's basically wipe it with oil all over and then run it around 300 for an hour or two.
As for where to start, I would suggest ribs. They tend to be more forgiving and are a little blander on their own. This will allow you to blend woods and other smoking material and learn what you like. I am partial to anything with apple in it. It's a New England thing maybe. Hickory I use like a carrier. Apple is my BB. And cherry is my BA. The size of the wood changes the taste as well. Compare a log to a lump to mulch and how quick each burns.
Once you learn the smokes you like, you need to learn to control the heat. Maybe it's easier with a propane smoker, no clue such a thing existed. But pay attention to the temp gauge.
A good thermocouple is a good investment. A thermopen works quick and easy. There are also Bluetooth probes that let you monitor from the phone.
After ribs, try whole chickens, or better yet spatchcock.
After that beef ribs.
After that you should be ready for brisket. Whole brisket too, you want the point not just the flat.
Lastly... Fuck sauce. Most BBQ sauce is shit. The only one I touch is James River BBQ sauce. It goes on ribs and chicken if I feel like it. So learn to season your gotdam food right.