Umm well
Order of operations is: PEMDAS which stands for Parentheses, Exponents, Multiple, Divide, Add, Subtract where you multiply/divide and add/subtract from left to right.
Inverse operations is what you have to do to undo what you just did lol
so if you add 2, to undo it you subtract 2 hynce addition/subtraction are inverse operations of eachother.
If you multiply 2, to undo it you divide 2 hynce multiplication/division are inverse operations of eachother.