Hey there!
To find x and y in the same equation, you either need to have the value for one of the terms (e.g. 2x = y, find x when y is 4) or you need to have a system of equations. A system of equations is simply two or more equations presented in the same situation and you can combine them different ways to find both x and y values for the situation, as it remains constant for all equations.
If you mean finding the value of variables in general, you use addition, subtraction, multiplication, and division to cancel out the terms and move them to the other side of the equal sign. For example, to find x:
2x + 4 = 8 (subtract 4 from both sides)
2x = 4 (divide both sides by 2)
x = 2
Hope this helped you out! :-)