When you have an equation with one unknown (a variable like x or something else) your main goal is to isolate the variable. Which means get the variable all by itself on one side of the equal sign. How do you do that? Well if you have a constant or a variable multipled by a set of parentheses you have to distribute the variable or constant: 3(x+3), distribute (multiply) the 3 to each element in the parentheses: 3x + 9.
Next remember you can add or subtract something from one side to the other: 3x+9=18; subtract 9 from both sides (opposite operation than it's original form to get rid of it on the right side (remember the goal is to get the x by itself)) 3x=9 then you can divide or multiply just like you can add or subtract from both sides. So if x is multipled by 3 you can do the opposite and divide both sides by 3 and you get x=3.
Sorry that was really long but I hope you understand how to solve simple equations like this a little better!