How to wire light switch?

Your question is very confusing. First off there are 3 type switches. A single pole switch, a 3-way switch, and a 4-way switch. Normal switches do not have wires attached to them. Only dimmer switches will have wires attached. If you have a black, green, and white wire coming out of the wall switch then what you have is a single pole switch wired with a switch leg. Take the dimmer switch back and purchase a single pole switch. Connect the green wire to the green ground screw on the switch. Connect the black wire to one screw and the white wire to the other screw. Make no difference which. Now if you are wanting to install a dimmer switch then you have purchased a dinner switch that can be used on a single pole or 3-way circuit. To connect it to your existing wires read the instructions that came with the switch. It will tell you exactly how to connect it. Or you can take it back and get a dimmer that is not a 3-way dimmer.

Step 1: Return the 3 way switch and get a regular switch.

Step 2: The green wire is ground, and the new switch may of may not have a ground wire.

Step 3: It doesn't actually matter which of the switch wires you connect to the black and which you connect to the white. The black in the wall SHOULD be the feed from the source, and the white the feed to whatever you are switching. The switch merely connects the 2 together, or disconnects them.