FAQ 2 - Startup / Group buffer

[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?
[2.2]: Gnus doesn't remember which groups I'm subscribed to, what's this?
[2.3]: How to change the format of the lines in Group buffer?
[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?
[2.5]: How to manually sort the groups in Group buffer? How to sort the groups in a topic?