If we use 6/8 as an example, there are 6 beats within one bar and the type of note that we count as the beat is the 8th note. However, depending on the tempo (how fast or slow), conductors will count in 2. Meaning they will wave a “beat” on beat one, and then wave a second “beat” on beat 4. So, in other words, instead of counting 6 individual beats, we divide it in half and count a “beat” on the first note of every group of three 8th notes. This larger “beat” is called the pulsation so that we don’t get our terminology confused with the 8th note beat. If you look at measures in 6/4 and 6/8, I have added accents to show where the pulsations are.
With time signature in 9 or 12, the same concept applies by dividing and counting the downbeats in every group of three. Therefore, 9/8 would have three pulsations, and 12/8 has 4 pulsations.
Does this make more sense?