Napoe82,
I've taught people how to do this before but never without giving audible examples so this may be kind of difficult. I'll give it a try.
Have you ever heard "We Will Rock You" by Queen? They play this song at alot of sporting events. Hopefully you have because this is a perfect example. The hook of the song goes "We will, we will rock you, rock you" and then repeats. Normally when this song is played people will stomp their feet along with it. Let's just look at the "We will, we will" part.
When the word "We" is said you stomp your feet twice. When "Will" is said you clap your hands once. You then repeat this whole process again. If you do this twice you now have completed one musical measure or bar. So two foot stomps (We), then one hand clap (Will), then two foot stomps (We), then one hand clap (Will) is equal to one musical bar.
There are four beats in a musical bar. In the above example the first "We" would be the 1st beat, the first "Will" would be the 2nd beat, the second "We" would be the 3rd beat and the second "Will" would be the 4th beat making one complete bar. Do this 16 times and you'll have a 16 bar.
Most producers make changes to the beat every 4 bars. This is helpful because rather than counting each bar you can just count the 4 bars instead. A hook, for instance, is usually (2) 4 bars repeating. Listen to any pop music and you'll be able to hear this.
Hopefully this is helpful as opposed to confusing. If you need further clarification let me know.
Stray