I play guitar and don't know what tempo it is?

[BobSubgenius]

Either that or you change the time signature of your Live set. In the top left of the screen where it says "4/4", just click on the numbers and write 6/8. It is in the same part of the screen as the tempo of the set.
Time signature changes can also be automated in arrangement view if you need to change during the song: https://www.ableton.com/en/manual/arrangement-view/ (scroll down a bit)

[ben1111]

Cheers Bob