You play the fourth and go up a semi-tone.

In key of C major: C D E F G A B C

You would play F#.

There is not one way to play it. For example with the root in the 6th string, you play one string down and one fret over to the right. That is only if the root is in the sixth. But aug 4 is just a note, in relation to whatever scale you are in.