Need help figuring out how to do a grid of pictures for my portfolio website!

I want a simple grid that is 2 by 2. 2 pictures on top and 2 on the bottom. I can’t figure out how to write the code to get the pictures to be in a grid layout, in the center of the page, and all the same size

What have you come up so far? Show us your code.
Are you using Bootstrap?
Check out Bootstrap, topics about containers, rows, columns for divs.