The most common meter in (Western) music is 4/4.
The denominator tells you that every beat has a value of a quarter note. The numerator, in this case also 4, tells you how many quarter notes there are in a measure.
So, there are 4 quarter notes per measure in 4/4.
Play the movie. Listen to the drums and tap your foot. This is the tempo or the beat of this song. Every tap is a beat, a quarter note.
Now listen to the other instruments. You will notice that ‘something’ changes every 4 beats. In this case the chord and bass note.
You'll notice that, after a while, the beats no longer correspond to the tapping of your foot, but some time later it matches again. It looks like we're dealing with half beats somewhere in this song.
In time signatures with full beats we use a 4 in the denominator. Since we are dealing with half beats, we'll divide the denominator by 2. 1/4 divided by 2 is 1/8. When searching for the numerator, we will have to adjust our way of counting. Instead of tapping every quarter note, we'll tap on every eighth note.