The following links provide a good overview of the features of the corpus.  Each link inputs values into the search interface and runs the query against the 400+ million word corpus (i.e. these are not "canned" results). You might want to note which options have been selected in the form, and then modify the values to create your own queries.

Using the web interface, you can search by words (grieved), phrases (of no little or faint + noun), lemmas (all forms of words, like sing or tall), wildcards (un*ly or r?n*), and more complex searches such as un-X-ed adjectives or a most + ADJ + NOUN. Notice that from the "frequency results" window you can click on the word or phrase to see it in context in this lower window. 

In terms of how you see the data, you can either see it in a chart display or as a list of the individual matching strings. For example, for the search ADJ fellow (fine fellow, smart fellows) the CHART display shows the overall frequency of all forms in each decade and it shows that there is a gradual decrease since the late 1800s). In the chart display, you can also see the frequency of the word or phrase in individual years as well, by clicking on the decade heading in the chart. The TABLE display, on the other hand, shows all of the matching strings. Within the table display, you can choose to either see the strings with or without the frequencies in each of the decades.

Sometimes -- such as when you are comparing two grammatical constructions, you will need to feed the data for the frequency of both constructions into a spreadsheet, and then generate in the spreadsheet a chart that shows the shift from one to the other. For example, consider the following:
 

Construction	Older construction	Newer construction	Chart
Future tense form	will V (I will do it)	going to V (I'm going to do it)	Click to see
Passive	be passive (he was fired)	get passive (he got fired)	Click to see
Relative pronoun	overt (the man that he saw)	zero (the man -- he saw)	Click to see
NEG placement with have	after (I haven't the time)	before with do (I don't have the time)	Click to see
Complement with start/begin	to V (started to leave): start begin	V-ing (started leaving): start begin	Click to see

You can also search for collocates (words nearby a given word), which often provides insight into the meaning of a given word.  For example, you can search for the most common nouns near thick, nouns after break (you can also sort by sorted by relevance: see examples), nouns after look into, or words with *strong* near men.

You can also sort and limit by the frequency in a certain time period -- a particular decade or set of decades.  For example, a basic search shows the overall frequency of all adjectives with girl, either overall or by decade. But you might want to see the most frequent strings in just one part of the corpus, such as the 1810s-1870s or the 1970s-2000s. (Notice that the selected decades have a different color, and that the SEC1 column at the right is the overall frequency in this set of decades).

Best of all, you can also compare one set of decades to another, such as the adjectives with girl that occur in the 1820s-1880s much more than the 1970s-2000s . Other examples are *ism words 1870s-1920s vs 1960s-2000s or collocates with gay 1860s-1910s vs 1960s-2000s. (Notice that in all of these cases, the older forms are on the left and the newer ones are on the right, although you could reverse this). The point is that you can compare anything in any sets of decades to look at language change.

You can also easily carry out semantically-oriented searches. At the most basic level, you can see the frequency of all synonyms of a given word -- such as beautiful or the verb clean or the noun trouble -- in each decade. You can also compare the frequency of synonyms in different periods, such as the synonyms of strong in the 1840s-1890s and the 1960s-2000s. You can use synonyms as part of a more complex query (such as synonyms of clean with nouns). Finally, you can create "customized lists" for any category that interests you, and then re-use these in subsequent queries (such as colors + clothes, or a synonym of stroke near a "body word").

Finally, you can search by individual genres (fiction, magazine, newspaper, other non-fiction) to compare the relative frequency of words, phrases, and grammatical constructions over time, and see in which genres the changes have been the most pronounced.

Hopefully this short five minute overview of the corpus has been helpful.  Now feel free to look at more examples of the types of possible searches, by clicking on any of the form elements (e.g. COLLOCATES or SECTIONS) in the search form.