Hi, and welcome to the forum.
My first muzzleloader was full of errors, not like my last one, that only had 492. But with patience you will get good like me
Seriously get one or several of the instruction books, or videos, and they will help a lot.
There are many builders about that will gladly get you started and keep you going.
Also study as many guns as possible, but when you are building one particular style of gun, focus only on that type.
When building, work on "one inch at a time" don't try to finish the gun in one evening. It will take many evenings to get it right.
Building a rifle from a stock blank, demands a lot of wood skills. And if you have no cabinetry skills, you will have your work cut out for you.
My first rifles the barrel channel was cut by chisel and scraper, after I mastered the use of the table saw and router, barrel channels are a breeze.
So good luck, and ask lots of questions.
Best regards
Old Ford