I am putting a light inside the passageway between 2 houses. i want to run the power from the indoor downstairs toilet light switch. The switch in the toilet is a single 1 way switch but i want to run the outside light on a seperate switch so i dont have to leave the light in the toilet on nor do i want to put a seperate switch and box on the wall. what type of double switche do i need? ..also could you explain what 1 gang 2 gang mean .. is a gang a switch ?
Your toilet switch is most likely just a switch-loop from the ceiling rose. Taking power from there will be, as JJ would say, a fluffcake.
You'll probably need to take the power from the ceiling fitting rather than the switch.
putting more than one socket or switch next to each other is called ganging so as you've figured, a single gang box is for one socket/switch, a double gang for two and so on.
Assuming it's the common installation method,whereby the lighting circuit loops at the fitting (ceiling rose) then you won't have a neutral at the light swtich, just a live and switched live. You need to get your power from the light fitting/ceiling rose.
Have a read here to learn more about lighting circuits; (aimed at the DIYer)