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The individual sets of functionality (such as the ones you listed) should be applications.
When you group several applications together, you form a project.
However, the individual applications are usually self-contained enough that they could be picked up and dropped into another application. In this manner, you can re-use your ‘login’ application in several projects.
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If it’s part of the same site or webapp you’re building, than don’t make another project, one project shares the same settings.py, for example, so you can imagine that everything that relates to it belongs to the same project.
About the apps, you can create an entire project with just one app, but that’s not advisable, you can separate your models in apps in a way that you fell confortable with it, for your own organization.
About login/register, take a look on User authentication documentation, that can clarify a little how one part of the site, in this case, authentication, can work with it’s own app.
You should also do the Tutorial which could help you to understant how django basically works.