Welcome to the platform @polplp !
Our YouTube channel (https://www.youtube.com/user/exocortex) is a great resource for the modelling basics, although I don't believe there are explicitly car modelling tutorials.
That being said, if you are more familiar with Rhino, you can always model some complex pieces externally and then import them into Clara.io (STEP or FBX files tend to maintain the highest fidelity).
You could even document the process so that others will benefit from what you've learned.
All the best,
Kiefer from Exocortex