90% of all modern pop music is in 4/4 time.
This means that when you listen to the song, you count 1,2,3,4 - 1,2,3,4
Most of the rest are done in 3/4 time 1,2,3 - 1,2,3 Think of a Waltz for a good example of this time signature. There are also many other sigunatures, but they are rare in Pop.
Now that I am back home I can give you a good example of the sound change from going to a "normal" beat to a backbeat.
The Police do this song in regular format. 1,2,3,4
UB40 does it with a strong backbeat 1,2,3,4
1 2 Every 3 breath 4 you 1 take 2 3 4 1
And 2 every 3 move 4 you 1 make 2 3 4
1 Every 2 bond 3 you 4 break, 1 every 2 step 3 you 4 take
I1 ’ll be 2 watch 3 ing 4 you
A back beat can make a different sound, but that is about it.