In the sentence
Ils savent tout faire.
what is the word faire? Is it a noun, as in They know everything, or a verb, as in They know (how to) do everything?
Also, tout is singular masculine, right?
Yes faire is a verb and tout is singular masculine but it does not really matter here. The translation would be "They know how to do everything" or "They are able to do everything", "They can do everything" ...