The menu on the left of the interface groups all your projects. If this list gets too long and you’re having trouble getting organized, you have several options.
Create project folders
In the left side menu, you can create folders to categorize projects.
To find out how to create a folder, see the article dedicated to project folders.
You can open or close a folder by clicking the arrow 
Archive a project
If you want to make the projects disappear from your menu because you don’t use them at the moment, you can archive them.
For more information, see the article on archiving a project.
Delete or leave a project
If you want, you can permanently delete a project or even a project folder.
Please note, if a folder is deleted, the projects (for which you are the creator or administrator) contained in the folder will also be deleted and will no longer be taken into account in calculating your statistics.
For more information, see the article on deleting a project.
If you do not want or cannot permanently delete a project, you can leave it.
You will then no longer be a member of the project, and it will no longer appear in your list of projects.
For more information, see the article on how to leave a project.