For any planar surface there is a horizontal line. You can relate that horizontal line to a compass direction.
If you were a drop of water on that horizontal line you'd flow down hill. Because the drop of water is starting from the axis of a horizontal line, the steepest path is perpendicular to the strike. The path of the drop of water is the "dip." That can be related to a compass direction also. The most typical convention for stating the strike and dip is in the form of NxxExxE or the many other permutations thereof. For example N 28 W 43E would convey that the horizontal line is directed 28 degrees west of true north and the dip direction is toward the east. (We don't get too precise on giving numerical values to the dip direction because it's defined as 90 degrees from the strike. We just let the audience know that the dip is to the east or west as there are only two choices.)
Relating this to the steronet is a whole different item. Imagine a piece of paper and a pencil sticking straight up from the center. As you change the strike and dip of the pad of paper, the pencil tip will move. If you were at the planetarium (i.e., like at your science museum), that pencil tip would point horizontal for a vertical pad and it'd point vertical for a horizontal pad. A steronet uses a map of a dome to show the location of such a pencil point sticking perpendicular from a planer surface. Geologists either use a "upper hemisphere" or "lower hemisphere" projection to do this. (The planetarium example would be the upper hemisphere example.)
Using steronets you can also enscribe a planer surface (i.e., use another mapping technique to show the entire plane rather than the point plot). This alternate mapping technique lets you map one plane against another plane and "see" where the line of intersection is located. This can fortess where a wedge failure may develop.
Please understand that all this is as precise as mother nature. Typically, we take a series of measurements, plot them all and look for trends. There are all sorts of ways to map concentrations in the population of data and identify likelihoods of failure trends.
When two planes intersect a line is formed. This line has a compass direction (trend) and an inclination (plunge). You use the same terminology for the map direction (i.e., N 28W) but the plunge is just shown as the inclination (23 degrees). The trend is always given looking downhill so the orientation of the plunge is understood.
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