Centering places an item around the middle of the space available to it. It is like putting a vase in the middle of a table so there is room on each side.
A logo might sit in the center of a welcome screen, or a short message might be centered inside a card. The item can be centered left-to-right, top-to-bottom, or both.
Centering every piece of text can make long reading difficult. Use it when the middle placement makes the content clearer, and keep paragraphs aligned in a way that is easy to follow.