Typically, a project is associated with something you'd like to achieve as a result of completing the project — the desired outcome. A project can be thought of as a complex task that cannot be completed in a single step.
Some important aspects of projects are:
Typically, the order of items is relevant.
A project can be completed.
Completed projects will be moved to the Logbook via Things' automatic clean-up.
Completed items “within” a project are not automatically cleaned up.
Projects cannot contain items from the Someday and Scheduled lists.
It's all right to have many small projects.
You can drag and drop the to-dos listed under a project to change the order in which they appear. This ensures that Things automatically places the appropriate to-dos in Next. Note that you can adjust the number of tasks that appear in Next.