PEMDAS is the order of mathematical stages to figure out a problem.
P: Parenthesis, this means you must figure out the problem within the parenthesis first before anything.
E: Exponent, exponents are, for example, x^2. You must simplify the exponents after the parenthesis, if any.
M: Multiply. This is simple, just do all the multiplication problems after you've dealt with parenthesis and exponents.
D: Divide, Divide out the problems after multiplying, if any.
A: Addition
S: Subtraction