1. The left side and right side in an expression usually refer to the two sides of an equation separated by an equals sign $=$. 2. To do left side right side checks, you compare the expressions on both sides to determine if they are equal or if they satisfy certain conditions. 3. For example, given an equation $A = B$, you can substitute values into variables in $A$ and $B$, then simplify each side separately. 4. After simplification, check if the left side expression equals the right side expression. 5. If they are equal for all values in the domain, the equation holds true; if not, it doesn't. 6. In summary, the steps are: (a) identify left and right sides, (b) substitute values if needed, (c) simplify both sides, (d) compare results, (e) conclude equality or inequality.