It appears you are dealing with a linear Diophantine equation in two variables x and y.
The third step involves using the one solution (x,y) that you already have to generate all of the solutions. To be specific, given the solution (x,y), all other solutions are given by
where . This means that for any choice of integer , the above pair gives you a solution to your equation, and vice versa, any solution to your equation is of the above form for some .