How do I install this light switch?

This looks like a heavy-duty use single pole snap switch. The screw on the bottom is for the green/bare wire. This is for grounding purposes. If you have two wires (black & white, two blacks, black & red) One of these should be the hot feed while the other wire should be the switch leg. On a single pole switch, it does not matter which wire goes where EXCEPT FOR THE GREEN/BARE WIRE!!!!!!!!!!!!!! This wire "shall" (must) attach to the green screw, Good luck and may God bless.

A regular switch is just an interrupter in most cases, meaning one of the black wires brings the power in, the other carries the load to the bulb.

First: the one at the bottom is the ground, so you will not run the risk of a shock. It is usually bare copper (in most homes).

Second: the two remaining wires you have, which ought to be both black, one brings the current in, the other takes it to the bulb. It does not matter which goes where, except that right on the switch button, one side is marked "on" and the other "off". If you connect them in the right sequence, the light ought to be on or off matching the switch button.

If you connect the wires and the light is off while the switch says on, no harm done. Just reverse them.

Note: one of the black wires brings the load in, so it is powered. Be sure to turn the proper circuit-breaker off before handling the wires, otherwise you will get a "hurrrr 110 V surprise" (lol).

In AC, there is no “positive” or “negative” because the current changes direction 100 (Europe) or 120 (America) times a second. Half the time, the hot wire is negative and the neutral wire is positive, vice versa the other half of the time. As for the switch, it doesn’t matter which way you connect the hot wires to the brass terminals. (You don’t connect neutral wires to a switch. If you see a white (America) or blue (Europe) wire connected to a switch, it’s not neutral.) The bare wire does indeed need to be connected to the green terminal, as EagleWatcher rightly pointed out.

There ISN'T a pos/neg on a switch. BOTH sides are 'hot' The screw at the bottom is a ground. The other two are interchangeable.

Looks to me like the bottom is the ground. It looks green.

i am from the u.k and we have different standards.

but try the cables one way around if it dosent work. it will blow a fuse/CMB/isolation falt divic so u tern the cables arounf and then it will work.

Why don't you check instructions from an expert?