When you purchase a domain from Yola, you become the owner of your domain name through the duration of the period for which you have purchased your domain name. You will receive a renewal notice before your domain expires. At that time, you can renew your domain, thereby, extending your ownership of that domain.
You can also choose not to renew your domain. If you go this route, then you will no longer have ownership of that domain name and it will be released for sale once again.