All the strumming patterns you have played so far involved playing a downward strum (a) on the first, second, third or fourth count. To make strumming more interesting, eighth note strum patterns can be used. An eighth note strum pattern uses a down and up strum within one count. An up strum is indicated by a s and is played on the "and" section of the count.
Play the following strum pattern, which has an up strum on the second beat.