Drafts are commonly applied to parts that are made with injection molding. A draft is a slight tilt between two different surfaces at different levels. In practice, drafts help to make parts fit better with the mold and make the part easier to remove from the mold compared to without it. Also, drafts help to increase the success rate of the mold taking effect. 

The following screenshots highlight the effect of the draft feature. The first screenshot shows the model at hand as well as the Cross-section we are applying to better show the effect of the draft:

The second screenshot shows the cross-section of the model With Draft and Without Draft. Note that the draft looks similar to a chamfer:

Now that we know what drafts are, we can move forward to applying the feature to create a certain 3D model.