Doth is a form of the word "do," which is defined as to perform an action. It is not used often any more.
An example of doth is "the lady doth protest too much" which means the lady is protesting so emphatically against something that it's likely she really likes whatever she is claiming to dislike.
Archaic do: chiefly as an auxiliary
Origin of dothsee doeth
A third person singular present tense of do1