You may want to review slope-intercept form first.
Suppose you have to find the equation of the line through (2, −4) with slope 2 ⁄ 3. (If the 2 were a 0, you'd already know how to do this.) The answer is y = (2 ⁄ 3)(x − 2) − 4. In general, you want y = (slope) (x + (x-coordinate with the sign switched)) + (y-coordinate).
Be careful always to switch the sign of the x-coordinate and never of the y-coordinate.