I need more resources for learning

Hello,

Background:
I’m making my first steps in WP and CSS.
I learned basic HTML (text, images, links, tables, frames)
I learned CSS using the excellent W3Schools.com.

Yet

My website at https://www.buy-and-benefit.com/ Looks terrible.

I want the blocks in the horizontal menu to have no spaces in between.
I want the nenu to be centered.
I want the text to be smaller.
I want to be able to solve all these problems and other alone ( I am most greatful for the help I get here). Yet, looking for a solution for every single new problem is not the perfect solution.
Colld you share some of your secrets with me and tell me how to learn css and apply it correctly?
Where can I find good resources? and guidance.

Thank you all,
Erez