There are four main operators.

+Which is used to add things together this can be strings(concatenation) or numbers.

-Which is used to subtract.

*Which is used to multiply which is done with Shift+8.

/Which is used as division(warning: when using division you probably want to use double datatype since ints will automatically round to a integer.)

Another operator although not common is the % operator.

%  is used to find the remainder from division so if you do 9%2 you would get 1. The % operator is Shift+5 by the way.This is mostly used to find is something is divisible by something.