You can think of an x-y edge meaning 'x is related to y'. If you use a one-way relation like 'is taller than', put an arrow on the edge to show which direction the relation is going. In particular, we can use graphs to describe computer networks. We use a vertex to represent each computer, and we put an edge between each pair of vertices that represent computers that are connected to each other. Note that it's not a very realistic map in terms of geography, but it is still useful in terms of the network.
Chemists use special kinds of graphs to represent chemicals.
A saturated hydrocarbon. Graphs are pretty good for puzzles, too. Try to find a 'clique' of 5 people in this graph. A clique in a graph is a set of vertices where every pair in the set are connected by edges. Use the BACK button on your browser to take you back to where you came from to get here.