They’re spring-loaded quick connect jacks. The wires go in the round holes not the rectangular ones. If you tug on them and they don’t come loose, then they should be connected properly. If they pop out, then you’ve just got to insert them further. I usually use my fingers, but you could also use something like needle-nose pliers to push one wire at a time into the hole until you feel it securely click into place. If you need to release them, put a small pointed tool like a tiny flat-blade screwdriver or some really pointy tweezers into the small rectangular hole next to the round one, and it will release the spring and allow you to remove the wire to try again.