A song with a time signature of 4/4 has four beats in a measure, and is counted like this: 1 2 3 4 1 2 3 4, etc. By far, 4/4 is the most common time signature you'll run into. In fact, 4/4 is so common that it is often called common time.
The time signature is written at the beginning of the staff after the clef and key signature. Time signatures consist of two numbers written like a fraction. The top number of the time signature tells you how many beats to count. This could be any number.
