I came here looking for making an input that's actually multiple lines. Turns out I didn't want an input, I wanted a textarea. You can set height or line-height as other answers specify, but it'll still just be one line of a textbox. If you want actual multiple lines, use a textarea instead. The following is an example of a 3-row textarea with a width of 500px (should be a good part of the page, not necessary to set this and will have to change it based on your requirements).
<textarea name="roleExplanation" style="width: 500px" rows="3">This role is for facility managers and holds the highest permissions in the application.</textarea>