This board features both Micro-USB and JST-PH power connectors, depending on whether you want to use a battery, but you must not connect them both at the same time. The through-hole JST-PH connector is also more firmly attached to the board than the Micro-USB. In an attempt to be compatible with Adafruit batteries, the ground pin is on the right when looking into the right-angle header.
These connectors and the larger JST-XH connectors are very popular but were a bit of a mystery. You buy them directly from JST. They are cheap. A couple of weeks later you have a little box of plastic and metal pieces. To make a connection you need the matching header, housing, and contacts. The header goes on the board, the contacts are crimped onto your wires, and clip permanently into the housing. You cannot make a proper crimp with pliers; you need a crimping tool. You can buy one from JST for about $489.89 but I bought this one. However you might want to look for one that is also compatible with slightly larger connectors.
Happily it appears that since the last time I looked JST's connectors are also available on Digikey. It's worth having a box or two of these around for whenever you need to make a wire to board connection.