Hello,
The main objective of CAD or Computer Aided Design for mechanical engineer is to provide an overview of how computers are being used in mechanical component design.
The important topics in CAD for mechanical engineer are

• Product cycle- Design process-
• Computer graphics co-ordinate systems- 2D and 3D transformations- homogeneous coordinates Line drawing -Clipping- viewing transformation
• Representation of curves- Hermite curve- Bezier curve- B-spline curves-rational curves
• Techniques for surface modeling  techniques- CSG and B-rep
• Hidden Line-Surface-Solid removal algorithms shading colouring computer animation.
• Assembly modelling
• Standards for computer graphics- Graphical Kernel System (GKS)

Hope it helps