You connect it according to the diagram that came with the switch. The bigger question is: Why did you delete the thread you started on fixing another problem that occurred when you installed the dimmer? You appear to have a complicated mix of wires in that box, and a simple answer to your newest question won't necessarily resolve a potentially hazardous situation.

you should always first label or take a photo of connections. make sure the dimmer is compatible with the type of light.

if you have no clue what youre doing, dont do electrical work.

that said,

youre going to have two sets of wires entering the box. One will have a black, white and a ground, the other will have a black, red, white and ground. The first set of wires are your feed or your switch leg. The 3 wire romex is your travelers to the next three way switch.

Both switches need to be wired exactly the same so you could take a look at the other one, but..

Both bare grounds tie together and then ground the switch (and the box if metal). The white wires which are neutral, bypass the switch and are wire nutted together in the back of the box. Your black wire from the set that doesn’t include a red goes to the black screw, put the red wire from the other set of wires above or below that on the gold screw and finally your other black wire will go opposite of the red wire on the other gold screw. make sure your wires are tightly wraped and closed around the screws and its also a good practice to wrap the switch conections with electrical tape to prevent a dead short if the bare ground were to bunch up and touch one of the hot terminals.

Thanks Dave, I got someone to come on and help me out so it's working correctly now.

There are (functionally) two styles of 3-way switch-dimmers. One has a dimmer on only one end of the system - you can turn it on or off from either end. The other, I think it's called the Maestro, has dimmers at both ends. I had those at my old house, but the builder of my new one were too cheap to use them!