You are not logged into your account (or have not yet signed up for WikiTree), so that would be step one!
From there, you will need to review the list of active Projects, and then decide if that project is already covered as a part of an existing top-level project, subproject of free-space project. The requirements are a bit different for each, and you didn't provide enough information to determine where your idea for a project might fall, so all I can provide is general info:
- Difference between projects, subprojects and free-space projects
- Help:Starting a Project