1. It can go both ways. Someone can be named Catherine, but call herself Katy. But it's also possible that someone who calls herself Katy is actually named/christened Katy. Just find out how each person prefers to be called first. 2. I guess you mean for example, "Katy, short for Catherine/Kathryn/Katherine". It can annoy someone if you assume a nickname is fine with them, or even assume their name is short for something. 3. A nickname can be almost anything. Commonly it's a variation on the name, but not always. Another short version of Catherine is Rina. 4. You'll know when to call a person by their nickname - follow the example of the people who know them as well as you do (eg. if you're friends but not very close). You can always ask about a nickname. I'll also add: some nicknames are just between one or two friends. eg. one friend calls me "Kruu", but only she is allowed to call me that. This comes from the shared history between friends. If a stranger started using that nickname it would feel uncomfortable and invasive. 5. Using first names for older people doesn't matter as much in Western society. But for a teacher or someone in authority, it's a bit too friendly to use a nickname. I don't advise doing so, unless they ask you to call them that. 6. Nicknames can be unlimited, but of course difficult to keep track of! Most people who use nicknames are happy with just a couple, at most.

My name is James, and the short version of my name is "Jim". However I never go by this name. I always introduce myself as "James", and everybody calls me "James". Only very rarely do people call me "Jim".

My real name is Steven, but I am often called Steve. I don't mind either one. Certain names are automatically associated with shortened versions such as Steven-Steve, Michael-Mike, Joseph-Joe, Katherine-Katy/Kate, Elizabeth-Liz, etc. If you are just meeting someone, for example, named Michael you can say "Hi, do you prefer to be called Michael or Mike?" If it is a formal setting, however, you will want to call them Mister or Misses and their last name. They will then tell you if they prefer to be called by their first name.

Norm is my nickname.

Bliz, Blitz, Blitzy, Blizy, Bleatzy :)