All the rhythm patterns you have played so far involved playing a downward strum (u), on the first, second, third and fourth beat. To make rhythm patterns more interesting, eighth note rhythm patterns can be used. An eighth note rhythm is 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 i, and is played on the "and" section of the count. To play an up strum start the strum at the first string (the thinnest string) 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).