The document describes the process of depth-first search (DFS) on a graph using an adjacency list representation. It shows the recursive DFS algorithm by stepping through an example graph with 8 nodes. At each step, it marks the currently visited node as visited, marks the predecessors, and makes recursive calls to visit neighboring unvisited nodes. This traces out the DFS tree, showing how the structure captures the recursive calls. It concludes that DFS finds valid paths in the graph and runs in O(V+E) time like breadth-first search when using an adjacency list.