Guns are a lot like guitars: when you're just learning, you don't have enough knowledge and experience to evaluate what works best for you. As you learn and progress, you'll work that out. Sometimes - often, even - you'll head down false paths, and may chase the equipment fairy all over before you find your personal ideal.
As with guitars, you can shorten that process with good instruction. As long as you have a serviceable weapon to work with, an experienced instructor can give you a foundation in fundamentals that will serve you well no matter what gun you have in your hand. They can also, through experience, help guide you to a firearm that would be a good match. Often, they have enough of a collection that you'll have the opportunity to try a variety of platforms before dropping your own coin on one. Instruction can also prevent you from developing bad habits that are much harder to get rid of after they've become fully ingrained.
Working with a friend that is an accomplished shooter can be helpful, but I highly recommend the services of a good instructor. Being able to perform a skill is one thing, being able to foster those abilities in someone else is a whole different skill set.
