Gentlemen:
If I may, there is a very good book written by Sam Fadala entitled The Complete Black Powder Handbook (3rd Edition). ISBN: 0873491750.
It is an exceptional good reference book. Get a copy and spend some quality time reading. There is a good section on flinters, there use, cleaning, and loading as well.
This is not to take away from the help the others are offering, but rather to supliment it.
This is how I started, and found that beacuse of the knowledge I learned from this book, and the others that were willing to take time to help me, I avioded a lot of pitfalls and frustration.
Just my thoughts
regards and all the best
R