When you open TilePlanner, you'll see an empty square room containing a light in the middle of the scene by default. You can start customizing any wall by clicking (or touching) it.
In the Layout Management section, you'll find additional articles that explain how to customize the room any way you want.
If you are working on an existing project, you can create a new project by clicking the New project button in the main toolbar:
Make sure you save the current project before creating a new one, if you don't want to lose it.
You can save up to 3 projects with a standard (free) account. Contact your firstname.lastname@example.org if you are interested in switching to a Professional profile to save more projects.