Graphs are important types of data structures. Instead of thinking of things in rows and columns (the way we would in a spreadsheet or a database) we think of things as nodes and edges. This page has a very brief description of a graph data structure and then a long list of things that can be done with graphs - cycling, sortinfg, spanning, searching. This page is meant to explor, not to learn - ollow the links, try running some of the code (click on the r'run in IDE button').