In most music, bar lines are drawn across the staff, dividing the music into sections called bars or measures. A double bar line signifies the end of an important section of music, while a final bar line is written at the end of a piece.
The top number indicates 4 beats per bar. The second number indicates that each beat is worth a quarter note.
At the beginning of each piece of music, after the treble clef, you will see two numbers. These numbers are called the time signature.
The time signature indicates the number of beats per bar (the top number) and the type of note receiving one beat (the bottom number). This means that the * time signature indicates four quarter notes per bar, as shown in the following example.