of course it does. Being first author usually means you did most of the work (or at least that's what people will assume), which basically means it was YOUR project. Being 2nd, 3rd, etc is still definitely impressive, but it still implies you were more of a supportive effort rather than the primary effort on the project (again, there are exceptions but this is what others will assume).
It is very difficult to get a first author paper, not because you have to be a pro-researcher or anything, but because it just takes so much time. If it was truly your project you have to hash out an idea, write a proposal, get IRB approval, run pilot studies, do your actual study, analyze results, write the paper, submit, revise, revise again, and again, and again (the submission/revision process can take a year oftentimes). All the while you need to check in with your PI along the way, and if he/she is a busy person this can hold you up as well. All told, it's tough to do this in < 3 years of med school.
You can do case reports and get first authorships, but I personally can't speak to how those are viewed in relation to clinical/basic science research