What is a cluster? Crocheting a cluster involves partially making a number of stitches, then joining those partial stitches during the last step of making the cluster. At the following links, there are photos or diagrams that can make it easy to learn how to do this type of crochet stitch.
How to do Clusters Made of Double Crochet:
How to do Clusters Made of Treble Stitches:
With 2-dc Clusters:
With 5-dc Clusters:
With a 7-dc Cluster:
With Treble Clusters:
With Double Treble Clusters: