Discontinuities (joints) in rock mass can be characterised by their direction, which included dip and dip direction. See this video    • How to Measure Dip and Dip Direction ...   to learn how to measure dip and dip direction. It is important to know how to interpret this type of data; and the first thing that a practitioner must know is how to draw great circles of discontinuities using a stereonet. Then, you can analyse the plot and, for example, use it to estimate the stability of rock slopes.
This video will explain how to draw two different sets of data on a stereonet.

If you feel confident about this concept then you can try to answer a few quiz questions in this video: Stereonet Quiz    • Stereonet Quiz | Learn how to Read St...  . If you would like to learn how to use software to draw great circles and poles then watch this video    • Tutorial 4: How to Plot Great Circles...