keep text in its box instead of going all across page?

hello,

making a row with 3 columns and a text box in each column.

If I type a long line of text in a box it will not stay in the text box it just keeps going across the page (and way outside its box) in preview. If I hit enter to break the line then then I get a new <p> and the lines are all double spaced.

Am trying to learn how to make padding around containers and elements especially because I don’t like how text goes all the way to the border/edge of the pages in some situations.

thanks!