Thin lenses — Draw

How is a ray diagram constructed to show the formation of a real image by a converging lens?

From the top of the object, draw one ray travelling parallel to the principal axis, which refracts through the lens and passes through the principal focus on the far side, and a second ray passing straight through the centre of the lens undeviated. The point where these two rays cross on the far side of the lens marks the top of the image, which is real (light actually converges there and it can be projected on a screen) and inverted.