Creating an account is free. To begin, go to the Corpus of Historical American English page, click on the Enter button, and register an account name and password (see link at upper right-hand corner of the page).
After this is done, read the accompanying short essay by Mark Davis on kinds of searches that the site enables. Then explore the website yourself. Read the whole article but focus in particular on Section 1, basic searching.
Start with a single word search or two, which will show you the frequency of that word's use by decade from 1810 to 2009 (!). Note how you can click on particular decades for examples, then explore those examples if you want to see the broader textual context in which your search word functioned. Then try search for a word string (a phrase), and after that doing some "collocations" (exploring which words most often were grouped with your search term, such as which adjectives tend to be paired with a particular noun). You can also explore the use of synonyms. Best of all, you can track how language use patterns change over time.
I didn't find the website particularly easy to use at first, but be patient: once you learn the ropes it's really fun to use! We will try out some "live" searches in class together, and then you can do more searching on your own--after which we can discuss what we can learn from the search results, what further questions we might ask, how we might apply such research to reading Cather, Hemingway, ex-slave narratives, or any other document, etc.
Note: "corpus" means "body"--in this case, a kind of body or digital archive of 450+ million words taken from a wide variety of print publications--from novels to periodicals to agricultural and medical publications, etc etc published in the U.S. between 1810 and 2009.