See Composite time signatures.
Compound meters, sometimes called triple meters, are time signatures whose rhythmic pulses occur in threes, such as , , and so on. See Time signatures for general instructions.
Note, however, that the way you define your triple meter is very important, because it also governs beaming in the region it affects. To beam eighth notes in groups of three, for example, the values of the notes in the Time Signature window for a 6/8 meter should be two dotted quarter notes, not six eighth notes; if it displayed six unbeamed eighth notes, you’d get no automatic beaming. In short: the lower buttons determine the rhythmic value of the pulse, including beaming groups; the upper buttons determine how many of that rhythmic value.