How do we know how many columns or rows that are required when you create a website using css grid ?
How do you know? Experience, I guess. The layout you want dictates the rows and columns, there is no universal “required” amount. However, if you are making an actual grid system to use, then 12 columns are commonly used.
I am finding that planning the grid based around the specific design goals I have for a site works well. Keeping the box model in mind, you can break down a site or a section of a site and make a grid to fit your needs.