The United States Geological Survey has been creating maps since 1884, and they're all available online for free.
Follow this link to an online library of historic maps of the Northeast. Find your state, click “Town Index,” then select your town name to view available maps.
This 12-minute video explains how to read contour lines and identify features like hills, cliffs, depressions, and drainages on a topo map. Jump to 9:20 for a summary.
This 3-page PDF shows all the symbols used in topo maps and what they mean, from the common (like streams) to the unusual (like cave entrances).