1. Go to the USGS Store. 

2. On the righthand side of the page, under Topo Maps, click on download to access the Map Locator.

3. Search for your area of interest, either by typing in a place name or zooming in and clicking on an area on the map.  For example, search for "St. Louis".

4. Add a red marker to the area of interest by clicking on the map.

5. Click on the red marker to see a pop-up showing available maps for that area.  Oftentimes there will be a few options, which correspond to the paper USGS topographic map series (7.5x7.5, 30x60. etc).  You can also see what year the map was created in.

6. Click download to download a zipped file to your computer.

7. Unzip and view.  The file format is a GeoPDF, which contain can be viewed in Adobe Acrobat.