Two more logical functions finish the set started by AND and OR.
NOT reverses a test: =NOT(B2="Closed") is TRUE for every status except Closed. It's most useful around another function, such as NOT(ISBLANK(C2)).
XOR, exclusive or, is TRUE when an odd number of its tests are TRUE. With two tests that means "one or the other, but not both": =XOR(B2>=100,C2="Member") is TRUE for a big order or a member, but FALSE for a member with a big order. With three tests, all three TRUE also gives TRUE, which surprises people.
Like AND and OR, both work on their own or as the test inside IF.