I am now starting my first iOS application.
It has a login-sreeen at beginning.
After Login screen there should be around 4-5 items (Tab Bar?!) what you can do there (e.g.: write a PM).
What template should I use when beginning with this?
What is the exact difference?
There is the cunningly named Tab Bar Application template
But to be honest with you; if you are just starting your first iOS application – worrying about what template to use is of lower priority than other questions. The templates provide a starting point, but you still have to fill in a lot of the detail. Don’t think that choosing the template means you only have to fill in a few details to flesh out your app.
Have you read any of the documentation? That is really what you should be doing and planning your application model rather than worrying about which template to use.