Motor Power connections on the Control Hub (REV-31-1595) use the JST VH style connector. This connector is keyed and locking with a small latch, seen below, which must be depressed to release the cable.
Figure 1: How to Use a JST VH Cable
REV Robotics recommends, in most cases, that teams use pre-made cables because crimp quality is better when made using industrial tooling. These cables can be purchased directly from the REV Robotics website or through other online vendors.