The very basic starting point of learning how to use Voyant should start by looking at these basic guidelines, which include creating a corpus (a collection of text), modifying the corpus, embedding Voyant into your website and export the text into the tool, and setting the default skins that include Cirrus (i.e., word cloud for keywords), Reader, Trends (i.e., keywords trending), Summary, and Context.
(Source: https://voyant-tools.org/docs/#!/guide/start)
You can use the feature called Stopwords to make a list of words that should be excluded from the results of the tool. Meanwhile, you can use the feature called Categories to list the words you are interested in. See below two links for details.
(Source: https://voyant-tools.org/docs/#!/guide/start)