This is a linear function which means a straight line graph. To draw the line we only need two points on the line. The easiest points are the intercepts, which are points on the x and y axes. When x=0 this is the y axis, and the equation becomes y=3, the y intercept. So mark 3 on the y axis. When y=0 we have x+3=0 so x=-3 is the x intercept so mark -3 on the x axis (left of the origin). Draw a line through these two intercepts and you have the graph of y=x+3.