Check the instructions for the GPS hardwire kit to be sure - usually the red wire is the power (red goes to a switched 12v lead) and black is ground.

The blue thing in the picture is a crimp connector and you just insert the red wire into the opening and using a crimp tool, pinch the blue part a couple times to hold the wire in place.

You can add multiple devices this way, and a GPS doesn't take a lot of power. It would be cleaner to run the wire from the piggy-back fuse device shown to a split connection that allows you to wire in each device.

I used a fuse panel to split the power into six different items. Then I connected the various devices to the fuse panel.