Hi. I downloaded PL/SQL Developer as a trial. I am unable to connect my database and do not see any helpful instructions. In other software I am testing (for example, DBeaver) there is a settings window where I enter the Host, Port, etc. However, I do not see where/how to do that in PL/SQL Developer. Any suggestions are appreciated.

PL/SQL Developer needs something else to be able to connect to a DB,
You can use a client DB or Instant client, both from oracle..

It is mentioned via Help -> User's Guide from the GUI. Section 3 is "Logging on to an Oracle database"