98 4runner limited trd keyless/alarm

Just bought a used 98 4runner ltd. Received only 1 key. key only works in ignition, not any of the doors. key has keyless remote controls as part of the key. standard lock/unlock. 3rd green button. anyone know what that's for?? I admit I don't know too much about how the typical toyota alarms work. it has a red pushbutton led just to the right of the instrument brightness knob. how does that thing work?? I've set to alarm off inadvertantly multiple times now messing with it, but can't figure any of it out. Please help me! The only key we have with the keyless stuff doesn't work too well either, anyone think that's just a battery problem?? And if so, do i gotta worry about resetting the key after changing the batt in it?
thanks,
dan

Sounds like your vehicle has been a theft recovery claim and they had to change out the locks from them being ruined.