What do you want to acheive? Open VST Live, make sure devices and MIDI/Audio ports are set up in the Hub. New Project, play - no sound? Check Layers and make sure Layer has a MIDI input assigned (your keyboard) so that the LED lits when you play. have an Instrument selected and make sure the instrument has a sound assigned. Now Meters in the Mixer should move and you shouild hear something. Unless you changed things it should work out of the box.
Not fixed at all, those are “just” delivered with VST Live and ready for you to use, but any VST 3 and even most VST 2 plugins are supported, and of course AU. Click on the Instrument item in a Layer, you should see all of your installed instrument plugins, no?
You may have to select the Tracks tab, select the track that doesn’t play, and extend the Inspector. There, make sure your plugin is selected. Note That VST Live does not automatically assign those from the VST Rack, only from Instrument Tracks.
It also really depends on what you want to acheive. If you want to play back stuff you recorded in Cubase, ex/import is the right start but it looks to me as if you just want to play. Use Layers, they are easy to program.