Could anyone help me out?

It is possible that I get the money for a gaming PC somewhat soon. And I have absolutey no idea about anything regarding PC gaming.

I was thinking about going to a electronic store and buy an already built set, because I don't trust my clumsy hands for the delicate process of building a machine, but I think some people don't recommend that and I don't know why would that be.

Any insight? I could do my own research, but I would like, if possible, that someone kindly explained this to me like I'm five. I can be dense.

Thanks in advance.