If you’re trying to run something like:
webserver-manager start
and your terminal is returning an error about not being able to find Java as an internal or external command you had the same problem as me! Yay, error friends. I was able to run:
java -version
and get a response, which means I did have Java installed. To solve the problem Selenium needs to have the JDK/bin folder manually added to your path. This GitHub issue helped solve my problem.