The equation of a line

The equation of a line has this form:
y=mx+c

m is the slope of the line, the amount it goes up (in the y direction) for every 1 it goes along (in the x direction).

c is the y-intercept - the y co-ordinate of the point where the line crosses the y-axis.

If you know one of these but not the other, and you do know a point (x,y) that is on the line, then you can substitute the values x and y for that point and get an equation that you can solve for the unknown m or c.