Basically, you should have knowledge of the following:
1. operations (Addition, Subtraction, Multiplication, Division)
2. the order of operations - so you can solve a number sentence with more than one operations involved.
3. Number system (real number, whole number, integers, natural number, rational, irrational, etc.)
4. Rules on operations on integers - how to solve signed numbers (positive and negative)
5. absolute value
6. In real life application problems (word problems), you must know how to transform the given problem to expression, then from it derive the equation based on the requirements of the problem
7. Practice, practice, practice :-)
The concepts are taught in grade school.
