Yes you can ! It is free and without any obligation.
First fill in the form on the ad that interests you starting with date and time of departure and return, and estimated number of kilometers you think you'll travel.
Click on "Contact the owner".
Sign up or log in to your account.
Leave a message to the owner with your phone number.
The owner will immediatly receive a text message with your phone number and will contact you within 48 hours.