The easy, intuitive way to use Wikivietlit categories is to start with an entry you are interested in, read the cluster of categories at the bottom, and follow one.
For instance, the brief entry on Le Ly Haslip carries this cluster of categories:
Authors | Memoirists| Memoirists of war in Viet Nam| Memoirists of exile | Memoirists of exile in the United States| Memoirists composing in English | Memoirists of war in Viet Nam composing in English| Memoirists of exile composing in English | Memoirists of exile in the United States composing in English | Translated into French | Translated from English into French | Translated into Italian | Translated from English into Italian | Born 1940-1949 | Woman | Woman born 1940-1949|Entries started by Hai-Dang Phan
If you were interested in Le Ly as one of the Memoirists of exile in the United States composing in English, a click on that category would list for links to Wikivietlit entries on Le Ly's peers.
The hard way to use categories is from Articles by Category, also accessed through the left-hand navigation bar of Wikivietlit. They are unwieldy, nearly 500 categories. Dan Duffy wrote them to assist intuitive searches from a single entry.