when you have a point, it is a coordinate pair. in other words, it represents an x coordinate and a y coordinate that go together. it says, for (x,y), when you put x into your equation, the result will be y. thus, you can just put your point for the x and y values in the equation.
ex. (1,6)
when x = 1, y = 6
6 = m(1) + b
hope this helps <3
