Here's a quick refresher on how musical rhythms are notated.

The basic unit of metrically notated time is the whole-note. The rhythm notation system divides the whole-note into smaller and smaller fractions, as show in Figure 1. As expected, two half-notes take up the same amount of time as a whole-note; four quarter-notes together are likewise the same length as a whole-note; and so on.

Written music is usually divided into bars or measures. Measures are separated from one another by a vertical line called a bar line.
Most music is written with a time signature at the beginning of the piece, the most common of which is 4/4. However there are also time signatures such as 3/4, 6/8, 2/2 and sometimes even 5/8 or 11/4. In print, a slash mark is used, which makes time signatures look like fractions -- but in fact they are not. In printed music, the first number is above the second one.

In each time signature, the first or upper number indicates how many beats there are in a measure, while the second or lower number indicates the type of note that is considered the beat. Most often, quarter-notes are used for the beat in which case the denominator is 4. Thus, in 4/4 time there are four beats per measure and each beat consists of a quarter-note.

When counting rhythms, you start over in each measure. For instance in 3/4 time, you would count "one-two-three, one-two-three." Counting eighth-notes in the same meter, you'd count "one-and, two-and, three-and." Thus, the second eighth-note is often referred to as the "and" of the beat.