Doctypes are used on every website, if you view the source of this page for example, you will see this at the top
- HTML: Select all
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
This tells the browser that it is a transitional doctype and should be rendered as such, the other alternative is a strict doctype.
The difference between the two is that a strict is harder to validate(get 100% correct code without any errors, I would start off placing a transitional doctype on your page and after you have fixed the errors you have got, then think about a strict doctype.
Hope this helps mate
Craig