General
Type your search terms in the four empty boxes, one or more per box. With the menus at the left of each box you can restrict to a specific field: author, title etc. The menus at the right determine what happens if the box contains more than one word:
all words: will return articles that contain all words, anywhere in the requested field
any word: will return articles that contain at least one of the words in the requested field
exact phrase: will return articles where the words appear as a continuous phrase in the requested field

Authors
Use the format smith_cp. Author names are automatically expanded to include all combinations of initials, e.g. smith_c returns Smith C, Smith CA etc. You can turn this off by using exact phrase (instead of all words/any word)

Date
You can restrict to recent articles (published within a certain number of days), or you can restrict by year of publication.

Show results
You can use these options to order the results by relevance or date of publication and display more or fewer matches per page.

Wildcards and truncation
A question mark stands for any single character. An asterisk stands for any number of characters. These wildcards can be used at the end of a search term, and also at the beginning or in the middle of a word. The search may be slower in these cases.
Examples:
tumo* retrieves tumor, tumour, tumors, tumours, tumorigenisis, tumoricidal etc.
nf* retrieves NF-κB, NFκB, NF-kB, NFkappaB, NF1 etc.
j*son retrieves Johnson, Jonson, Janson, Jenson, Jackson, Johanson etc.
j?nson retrieves Jonson, Janson, Jenson etc., but not Johnson.