I don't quite agree with Judith. In my opinion it's simply a grammar question whether there's a 'zu' in a sentence, but that doesn't have anything to do with the verb or change its meaning - just like in English you sometimes have 'to' + verb and sometimes just a "naked" verb. You "only" have to know whether the construction in your sentence requires 'zu'. For example: - Das kannst du tun. - Das brauchst du nicht zu tun. There's no difference in meaning for 'tun' here, the 'zu' is just there because the '(nicht) brauchen' requires it.

"tun" is "to do/ to make" in English, "zu tun" is "to have to" or "to do with" e.g. Das hat wenig damit zu tun : It has little to do with that Was kann ich tun? What can I do?

''Zu'' means ''to'' you place it as you do it in English with one exception: You don't use it with the modal verbs