The AND Gate has two inputs and one output. The output will turn on when both inputs are on. This can be useful if you want to make sure nobody else uses your pressure plate because you can turn the Lever off when you are finished with the pressure plate so no other players can use it. Doing this will help combat issues with other players on your base without blacklisting.
Signal Inverters and AND gates put together can make a NAND gate.
A = Left input
B = Right input
0 = Off
1 = On