A space when beginning to write an essay.
When writing a business letter, you usualy don't indent.
I never have. It's standard practice not to indent in Internet writing.
Yes, you indent whenever it is the start of another paragraph. It doesn't matter what type of writing it is, you always indent at the start of a new paragraph.
No, but you do indent in a friendly letter.
There are no rules for indenting in a personal letter. If you want it to look neat and want the reader to be able to discern where one subject stops and another begins, then an indent would be a good idea.
When you are starting a new paragraph. The first word of that paragraph MUST be indented.
Yes, you indent each new paragraph.
By pressing the Tab button :)
No
At the beginning of each paragraph (except for the first paragraph if you start with a really big letter like they do in some books.)
The full block format does not indent.
Yes you do. You don't in a business letter.