Open the projects page and click the "+ New Project" button.
A dialog will pop up asking for a Project Name a Short Label and color.
The short label will be displayed instead of the long name in some places, so be careful to pick short and long names that have a similar meaning.

In the projects list click the icon to open the project details page, then click the icon near the name of the project.

The Project has the following attributes:
Project label, short label, description, color, cost per hour and archiving status.

Click the icon of the task you want to edit.

The Project has the following attributes:
Task label, short label, description, color, cost (billable or non billable) and archiving status.

Archived projects and tasks will not be downloaded by your watch, and they will not be visible on some lists on the website.

Archived projects and tasks will appear on reports, the cost of the projects, the billable attribute of the tasks and all time entries registered to them will be computed.

To archive or activate an item click the icon. This function is available at the project/task details page, and there are also some shortcuts to it on various lists on the website.

Projects and Tasks cannot be deleted.
But you are free to change all attributes including cost, name, and color.

The reason for that is simple. If you modify a project or task by mistake, it's straightforward to fix the error adjusting it again with the correct value.

BUT DELETION IS FOREVER! And you don't want to delete by mistake an important project or task that has hundreds of hours logged.