Here is detailed information on how to add your Toontrack product as a plug-in in REAPER.
This guide was made using the mac REAPER version 6.69.
First open the Track menu and select insert virtual instrument on new track.
A dialog will then open where you can select the 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 Track menu.
Then open the FX menu and choose the effect plug-in to add, click Add.