First, find the slope of the line between the two points by using the slope formula, (y2-y1)/(x2-x1).
After finding the slope, (m), use the point-slope formula with the m you found and the coordinates of either one of the points. Formula is y-y1 = m(x-x1).
Plug in m (the slope you found), y1 (the y coordinate of one point), and x1 (the x-coordinate of the same point.) Now you will have an equation of the line, you'll just need to rearrange it into Ax + By = C form. Good luck!