Rhythm Recall is one of the most free form exercises we have, so it can take a little getting used to.
In Rhythm Recall, a set of tones will sound. These tones are played over a beat. Listen to the tones and remember how long they are played, and when they change. Next, replay that same set of tones. To start, press and hold down a key for the same amount of time as the first note. Then release the key when the note should end. If there are more notes in the set, press another key and then release it when the next note should end. Press the same key if the note is the same.
For more information about Rhythm Recall, please check out this page.