I have three black wires and a red wire. I also have three white wires twistef together and capped. Also, I have two ground wires twisted together . Now,I havetwo on/off switches I am replacing, when I took them out the red and black wires were on the switch that controlled the light one of the black wires was on the other switch that controls the fan. The third black wire was tied into both of the light switches. Now I am lost. My new dimmrd switch has two black and one green. What should I do.

The two dimmer wires connect to the red and black. Did you make note of how the wires were connected or did you just take all of them off? Dimmer switches wire like ordinary switches. Do you have a metal box? Are there bare wires in the box? The green wire is a ground only... to the metal box or to other green or bare wires in the box.