Starts with/Browse takes you to a particular spot in an alphabetical list of all of the titles, subjects, call numbers, etc., in the Library Catalog.
Browsing by title is helpful for items that come in multiple series, or where a variation in spelling or phrasing might affect a search. See, for example, the Dictionary of Literary Biography.
Note: HOLLIS may use different alphabetization rules than you are used to from other systems, in particular for numbers, symbols, and other special characters. This means you may notice minor variations in the order in which titles appear. For example, some systems treat "&" as equivalent to "and"; HOLLIS alphabetizes the ampersand symbol separately, ahead of numbers, meaning that Town & Country is not adjacent to Town and City.
Browse by subject to see how your topic is organized and subdivided in the Library Catalog's subject headings. See, for example, Isaac Newton.
Library Catalog records use subjects from a handful of well-controlled but complex taxonomies. Only the three most common display in Library Catalog records: they are the Library of Congress Subject Headings, FAST, and the National Library of Medicine (MeSH). The other taxonomies are indexed for search and may show up in the Subject filter. There are often several pertinent subject terms for a given topic.
(In "Catalog & Articles," you will see a huge variety of subject headings, and many apparent duplicates. Catalog & Articles' subjects, which are not available for browsing, come from much larger and less controlled array of taxonomies.)
Pro tip: It's often best to take elements from the subject headings and subheadings you see in your "starts with" list and incorporate them into a new search. From Advanced Search, select "subject" from the "any field" drop-down and add different combinations of subjects and subheadings. For example, the search "comic books, strips, etc." captures both underground comic books, strips, etc. and science fiction comic books, strips, etc.
Browsing by call number uses the logic of the library's physical arrangement of items to discover additional material on your topic. It's like looking at an imaginary shelf where nothing is checked out, nothing is in off-site storage, and everything is in the same building.
For example, you can use Library of Congress call numbers to browse materials by and about John Steinbeck across multiple libraries, or you can use Harvard-specific call numbers to browse Houghton's American manuscripts or the reference collection in Widener's Loker Reading Room. (For Harvard-specific call numbers, you also have the option to explore via search with Code: Local Call Number.)
To browse by call number, enter all spaces and punctuation as they appear in your starting call number. If you don't find the call number system you want on the drop-down list, choose "other."
Note: a call number browse is useful but not exhaustive, as some items in Harvard's collections do not have call numbers.