As a beginning 'smith, the most logical and practical process is to work for an existing gun shop and/or knowledgeable 'smith.
As a "general" gunsmith, you'll get a good selection of firearms to work with and to learn from. Working under an existing general 'smith, or even one who specializes is also a good way to go... you'll learn things you would never learn in the classroom.
Oddly, in most general gun shops that have a in house 'smith, much of what you will do is install sights, grips, accessories, detail strip and lubricate guns, repair range guns if they have a range... and inspect guns for safe function.
Until you develop a reputation, or do work for a known 'smith that trusts you, no one is going to give you any part of a high-end job to do. Specialization is not a bad thing, but can limit your potential until you get a reputation as a known specialist 'smith.
Once you've learned the business in the real world and have developed a reputation for quality and fair business practices... there 'ya go.
Good luck with it.