look at the ss below

When evaluating an algebraic expression the first thing you do is that you observe what would be the first operation applied on the expression.

In order to determine that you need to know the basic concept of PEMDAS

Where as  

P stands for Parentheses (brackets)

E stands for exponents

M stands for multiplication

D stands for division

A stands for addition  

S stands for subtraction

This is the order that needs to be kept in mind while solving the expression