You can create an OpenTreeMap account by clicking the "Sign Up" button on www.opentreemap.org or by clicking here.
The Account Creation form asks for several pieces of information. Some fields are optional. The required fields are: username, email address, and password.
After clicking: "Create Account", you will receive a confirmation email with a link to activate your account. Once you have clicked the activation link, you can begin mapping with OpenTreeMap.