To become a WWOOFer you must create an account, then select Become a WWOOFer.
You will be asked to provide details about yourself, as well as contact information (not shared with the hosts). Make sure to go through every step, including uploading a photo of yourself, and paying your membership fee. Each WWOOFer is required to have a valid membership during their stay. If you plan to WWOOF with someone, some countries offer a discounted dual membership for two.
Once you’ve paid the fee, you will be able to start sending visit requests to hosts to organize your stays.
If you want to visit more than one country, you will need to pay the membership fee for all pertinent organisations.
WWOOF organizations operate mostly on a national basis but collaborate internationally through the Federation of WWOOF Organisations (FoWO). By paying a membership fee, you are joining that particular WWOOF organization. You are welcome to join as many WWOOF organizations as you like.