plug in any value x and you will get a y value; plot the point (it's wise to pick a point close to x=0)

do this again and just connect both points and you will get the graph.

e.g.

let's try x = 0

y = 0 - 3

y = -3

so we have one point (0, -3)

let's try another value for x = 1

y = 1 - 3

y = -2

we have the second point (1, -2)

plot these points on a graph and draw a line passing through these points.