All the rhythm patterns you have played so far use a downward strum (t), on the first, second, third and fourth beat. To make rhythm patterns more interesting, up strums can also be used. An eighth note rhythm uses a combination of a down and an up strum within one beat. The downstrum "on the beat" is played louder than the upstrum which is "off the beat".
An up strum is indicated by a y, and is played on the "and" section of the count. To play an up strum start the strum at the first string (the thinnest) and strum all six strings.
There are two eighth note strums per beat. There are 8 eighth note strums in one bar of music in * time.
The downstrum "on the beat" is played louder than the upstrum which is "off the beat" (the "+" section of the count).