Sometime my gas hand works and sometimes it doesn't what can i do

Several possibilities. Todays gas is prone to gum up if not used up within a month or so, and if it does, it can cause the sender unit in the tank to stick. More likely, though, is a poor electrical connection, either in the dash cluster where the main harness plugs in, or in any one of the several connectors between the dash and the tank. The gauge itself can have a cracked wire, and older cars had an instrument cluster voltage regulator but I think they stopped doing that. Not much help I guess, but the idea is you must run some tests. When the gauge is not working, you can find the wire going to the sender and short it to ground. If the gauge rises the sender is probably the problem (unless the tank is empty, lol). If the gauge doesn't move, either it has failed or the power going to it has failed. Really simple circuit= 12+ to one side of gauge and other wire to sender which is a variable ground.