Here is detailed information on how to add your Toontrack product as a plug-in in Cubase.
This guide was made using the mac Cubase version 13.0.10.
First open the Project menu and select Add Track > Instrument.
A dialog will then open where you can select the VST instrument plug-in to insert.
In the dialog that opens. Select the Toontrack Plug-in you want to add in the Instrument list and then click Add Track. The plug-in will automatically open.
To add an effect plug-in, you first need a track, so add some type of track that outputs audio via the Project menu (audio track, instrument track).
One way to then add an effect plug-in to the track would be to open the channel settings (the e button icon on the track) and then add the effect in one of the effect slots to the left.