The photo above shows a closeup look at a cluster in progress, that is made of five double crochet. This can be helpful in learning how to crochet a cluster.
To make a cluster: Keep the last loop of each double crochet on the hook (in other words, do the usual steps in making a double crochet but do not do the last step; instead leave that loop on the hook). For a 5-dc cluster (as in the photo above), do 5 double crochet in this manner, leaving the last loop of each double crochet on the hook (as shown in the photo) then, yarn over hook and pull that loop (all at once) through all the loops left on the hook, next: chain 1 to close the cluster.
Note: The chain-1 to close the cluster does not count for any chains that you are instructed to make after the cluster. In this pattern, a chain-3 often follows the cluster, so you will do a chain to close the cluster then make 3 more chains to form the chain-3.
If you need further help with learning how to crochet a cluster, you may find it helpful to take a look at the How To Crochet A 2-dc Cluster (see link in Step 3). This spells out the full step-by-step instructions for making the cluster's double crochet stitches (with the last step of each not completed to leave that loop on the hook). The double crochet stitches would be made in the same manner for a 5-dc cluster.
Next Photo ---> Row 4