These graphs have an identical structure, but their nodes have been reordered. Fill in the corresponding letters in the corresponding nodes. Note that it only matters which nodes are connected with straight lines. The lengths of the lines, and which lines cross, are irrelevant.
Puzzles in this genre
In this example puzzle, there are only two nodes that are connected to exactly one other node. They are A and F. Of these, only one (A) is connected to a node which is connected to exactly one other node (B). These same properties are easily identified in the other graph, so we can fill in A, B and F. Next, we also know that F must be connected to E. Of the two remaining nodes, only C is connected to B. The last one must be D.