The Advanced Search allows you to do full-text searches of the books in the Library. To quickly find an author or title use the "Find Author/Title" box which is like an old fashioned card catalog of the Library's holdings or select The Library/Authors (by Historical Period).
1. To find the author "John Locke" (or rather to find the bio page for John Locke) it is best to use his surname "Locke". This produces 10 titles which are matched (the name "Locke" is part of the title), 13 people matched (most because the name "Locke" is part of the metadata about those other authors - Locke was influenced by them or Locke in turn influenced later writers), and 3 Groups were matched (because "Locke" was assigned to one of those groups, such as the Debate about the Divine Right of Kings). The John Locke bio page is linked to from the list of 13 people matches.
2. Alternatively you can go to The Library/Authors (by Historical Period) and browse the list alphabetically (select "L" for Locke) or by historical period (select Early Modern Period for Locke).