They make crimping tools for the pins, but if you are careful you can do it with needle nose. Cut the wires to length. Slip over the yellow weather proof seal. Then strip the last 1/8" or so of the wire, and push the seal to the edge of that. Lay the wire into the pin, and crimp the upper tangs around the wire tightly. You have to be careful to retain a nice round shape, if you smash it flat it won't fit into the connector. Once that is crimped slide the seal up and crimp the second set of tangs (strain relief) to hold the seal. Pull back on the wire and make sure it is nice and tight in the pin so it doesn't pull out accidentally later on. The wires push into the connector from the back, you will feel it click into place, they only go in one way. The red parts look like retainers that either will go over the face or the back of the connector (they are slightly different than what I use).
Here I just made one to show you what it should look like when crimped.
Use a bit of dielectric grease when reassembling. These connectors are good but not the greatest for keeping out water, deutsche connectors would be optimal in this situation.