Hey there dear Anon! It is not a dumb question at all, so do not worry about it.

What I do first is pick an aesthetic I want to make a layout of and go to Pinterest or Tumblr for images/research said aesthetic. Secondly and most importantly is the colors. I do a gradient map which really helps in making everything consistent. I use the gradient map on Photopea which is free! For the dimensions, you can download my banner and make your own with said dimensions if that helps you ^^ I use some resources for symbols such as /aosymbols and many more I can send you!

I hope this helps you and do not forget to find your editing style 🩶