A user can either scroll down the list of over 1,500 record collections, or narrow the search by searching for a specific locality or topic (using the "Filter by collection name" field in the upper left corner of the sidebar) or by using location, date or collection filters in the left-hand sidebar.
In the screen below, I started typing "massachusetts" into the "Filter by collection name" field. The list of 17 collections with "Massachusetts" in their title:
Alternatively, I could choose the "United States" link from the Place filter list, then pick "Massachusetts" from the list of states that appear:
If I select "Massachusetts" from the list of U.S. states, I get the same list of Massachusetts collections:
Note that the list includes collections with photo icons to the left of the collection name - those collections have record images. Some collections have a number in the "Records" column - those collections are indexed. Some collections say "Browse images" in the "Records" column - those collections are not indexed (see Post 3 in this series).
In the screen above, I right-clicked the link for the first collection listed. I can Open the link in a new Tab, in a new Window, etc. Why would I want to do this? Because FamilySearch does not keep the filtered collection list in the browser stack - if I come back to the Historical Record Collections list (by using the browser back button), I get the entire list of over 1,500 collections and have to enter my filters again. So I open a specific collection in a new Tab, and then can come back to the list of filtered collections in its own Tab.
In the selected record collection, I can enter search parameters into the search form for my person of interest. In the screen below, I entered a first name (Isaac), a last name (Seaver), a Birthplace (Massachusetts), and a birth year range (1820 to 1825):
I clicked on the "Search" button and there were two matches, both of which are for my 2nd-great-grandfather: