How exactly does evolution work?

I'm really sorry if this is a stupid question, but I got a bit lost while learning.

I was learning about mutations and from what I understood, somatic mutations are not inherited, while generative mutations are.

And if I understand evolution correctly, it works on the basis of mutations. And this is where I start to get lost, because don't changes in the spine or skin (etc) concern somatic cells? So they shouldn't be inherited? But then again, everything is in DNA, so it's possible? I don't know.

I feel like everything I've learned has gotten mixed up and I'm no longer sure how this all works, let alone evolution.

Can anyone help me understand it? I would really appreciate it.