When you open Cubase you MUST open a new project.

Then select 24 track audio for example... unless yoou are doing MIDI record and playback.

Then open up a mixer panel and select a channel to read or connect to a file.

There are too many options to describe and the "says its ready to go " is not enough information to know where you are.

You may have to imprt files or record music... Don't forget to select a track on the display of tracks.