Hello Aaron and welcome to the forum.
To learn a language and improve your vocabulary, you need to practice. Start reading, writing, listening, speaking. Try to watch a Japanese TV show and write down some of the vocabularies that you hear often in the show. Try to use the vocabulary by speaking with a Japanese native speaker online. There are a lot of websites where you can meet people who want to learn Japanese. The most important step to improve your vocabulary is to use the vocabulary that you learned, therefore, you have to find someone who speaks Japanese to speak with him/her.