The slope-intercept form of the equation of a line is
y = mx + b
1) Use the two points to find the slope.
Subtract the y-coordinates.
Subtract the x-coordinates int eh same order.
Divide the difference in y by the difference in x.
That is the slope, m.
2) Now you need to find b.
Rewrite y = mx + b with your value of m in the equation.
Now use one of the two points and replace x and y with the x- and y-coordinates and solve for b.
3) Finally, rewrite y = mx + b with the values of m and b you found.