Several questions:

What state do you live in? Rules very state to state. Some states have a roster of guns, you may only purchase approved firearms. Also, there may be age minimums for purchasing firearms. What is the purpose for this firearm? Concealed carry, home defense? Funsies? Who will be using it? Budget?

What ever you get follow safety rules:

Keep the firearm pointed in a safe direction. Never point the muzzle at something you are not willing to destroy. Keep the finger off the trigger unless you are ready to fire. Treat all firearms as if they are loaded.

Additionally, buy lots of ammo and practice, practice, practice!! Maybe join a shooting club to learn more and get training.