How do I level all my content?

This is my first post on the site, I'm still learning some basics. So I found some html/CSS exercises online and tried to copy them and so far so good but I can't level all my content and I'm not sure what to do This is the original and this is what I have

the menus and last posts are not on the same level as the articles. Why and how to fix it? I tried playing around with clear and padding and margins..etc..nothing This is my CSS

this is the html(1and 2)

TIA