Time Signatures with "8"
Up until this point, you have either been counting measures using the quarter note (4) or the half note (2) as the beat.  Time signatures with an “8” in the bottom slot use the EIGHTH NOTE as the beat.  In these time signatures, you get a swingy, fun kind of feel in the music.  The most common time signatures with an “8” in the bottom are 6/8, 9/8 and 12/8. 

 Here is what 6/8 looks like:

 1-2-3-4-5-6

Just like any other time signature, the top number tells you how many beats are in a measure, so in this case, this measure would get 6 beats.  The bottom number tells you that the eighth note gets the beat.  So the counts for this measure would be, 1-2-3-4-5-6. 
 
It is important to remember how many eighth notes equal other notes.  Time signatures with “8” in the bottom are all about SUBDIVIDING, remember, dividing notes into their smaller parts.  When counting 6/8 measures, you use your knowledge about eighth note combinations from 4/4, and apply it to 6/8. 

Let’s look at this example:

1-2-3-456

Notice that there is a dotted quarter note in this measure.  Since we are in 6/8, where the eighth note gets the beat, the note VALUE of the dotted quarter note is 3 beats.  So the counts for this measure would be 1-2-3-456.
 
Here is a chart to help you compare:
Type of note       “4” Time Signatures                “2” Time Signatures       “8” Time Signatures
Whole                         4 beats                                 2 beats                                    8 beats
Half                             2 beats                                 1 beat                                      4 beats
Quarter                       1 beat                                   ½ beat                                     2 beats
Eighth                         ½ beat                                  ¼ beat                                     1 beat
Sixteenth                     ¼ beat                                  1/8 beat                                   ½ beat
Dotted quarter             1 ½ beats                             ¾ beat                                     3 beats
Dotted half                   3 beats                                 1 ½ beats                                6 beats
 
With all time signatures that have an “8” in the bottom, these beats apply. 

Let’s look at a measure of 12/8:

 1-2-3-456-7-8-9-101112

The counts for this measure would be 1-2-3-456-7-8-9-101112.  The rest values are also the same as the note values, just like in every other time signature.  The same rules apply in 3/8 and in 9/8 as well. 

Here is an example of 9/8:

123-456-789

The counts for this measure would be 123-456-789.  Remember to SUBDIVIDE!

Lastly, when dealing with sixteenth notes in an "8" time signature, you count them like you would 8th notes in a regular time signature, with "&"s as the upbeats:

 1-2-3-4&-5&-6&.  See, every other sixteenth note is an "&", denoting the upbeats.

Just like in any time signature, the most important thing to remember is:

Make sure the measure is the correct number of beats according to the top number!