Fraunhofer diffraction: The diffraction in which the source and screen are placed at a greater distance (i.e., maybe infinite) from the obstacle is called Fraunhofer diffraction. A converging lens is used to focus the light coming from an infinite source to the obstacle and another converging lens is used to focus the diffracted light on the screen. In this type of diffraction, the incident, as well as the diffracted wavefronts are plane.
For the construction of Diffraction Grating refer to this question.