The time signature tells musicians how many beats of music there are to a bar and, often, how many beats per minute are played---which indicates the tempo of the song. 4/4 in a time signature indicates there will be four quarter beats to a bar. Those beats can be counted using any combination of note durations, such as whole notes, half notes, quarter notes, eighth notes or sixteenth notes. You can become familiar with note values by obtaining a beginning music theory book or by taking advantage of one of the many free websites that offer music theory instruction (see Resources).
Use a metronome to help you keep time. You can purchase one at any music store. A metronome keeps time with a clicking sound set to whatever tempo you choose. In the beginning, set your metronome at about 60 beats per minute. This is a slow enough tempo to allow you to keep up with your counts until you get a feel for the rhythm. Start the metronome and listen to the ticks until you have counted to eight. Start counting on the ninth beat. Hold the count for a total of four ticks, or beats. Do this four times, which will represent four bars of music. The count will look like this: 1. . . 2 . . . 3 . . . 4 . . . You'll start a new count on each number and hold the count for each period.
Half notes in common time are held for two beats. Keep your metronome set at 60 beats per minute, let a measure go by and then count 1 and, 2 and, 3 and, 4 and. You will count the number and hold the count for the length. Make sure you start the count on the tick of the metronome. Do this for several measures, each lasting a length of four beats, with you only counting on beat one and beat three.
In common time, you will play or sing a quarter note on every beat of the metronome. Start at one and count 1, 2, 3, 4, 1, 2, 3, 4. Do this several times, until you have a feel for the rhythm. This is often the simplest note for beginners to learn because it is simple counting. Every beat of the measure gets a note.
With your metronome still set at 60 beats per minute, start counting on the first beat with 1 and, 2 and, 3 and, 4 and. Only tap your foot on the tick of the metronome, but count both the number and the "and." These two counts together are eighth notes. There will be eight of them in one bar of music. Slow your metronome down if you feel overwhelmed trying this exercise; then bring it back up when you feel more confident.
Practice these exercises at 60 beats a minute using a combination of note values and equal value rests (silent periods). Try a round of two quarter notes, two eighth notes, and another quarter. It will look like this: tap, tap, taptap, tap. Each tap is a count. Try another: taptap, taptap, tap 2 3 4. Hold the last count out for the length of the numbers and you have a half note. Raise the tempo of your metronome when you feel more comfortable. You will also want to use simple sheet music and practice counting the notated music. You can purchase simple piano music at a music store or use one of the many free websites that provide simple piano music (see Resources).