FAQ 2 - Startup / Group buffer

FAQ 2-1: Every time I start Gnus I get a message "Gnus auto-save file exists. Do you want to read it?", what does this mean and how to prevent it?
FAQ 2-2: Gnus doesn't remember which groups I'm subscribed to, what's this?
FAQ 2-3: How to change the format of the lines in Group buffer?
FAQ 2-4: My group buffer becomes a bit crowded, is there a way to sort my groups into categories so I can easier browse through them?
FAQ 2-5: How to manually sort the groups in Group buffer? How to sort the groups in a topic?