can't understand csplit without examples

[Dan Jacobson]

csplit info page:
`N'
     Create an output file containing the input up to but not including
     line N (a positive integer).  If followed by a repeat count, also
     create an output file containing the next N lines of the input
     file once for each repeat.
Add an example.

`/REGEXP/[OFFSET]'
     Create an output file containing the current line up to (but not
     including) the next line of the input file that contains a match
     for REGEXP.  The optional OFFSET is an integer.  If it is given,
     the input up to (but not including) the matching line plus or
     minus OFFSET is put into the output file, and the line after that
     begins the next section of input.

Even more abstruse without examples.  Say how to split a mailbox into
one file per message.
$ cat mailbox|csplit - /^From/
is apparently way far away from whatever one is supposed to use.

`%REGEXP%[OFFSET]'
     Like the previous type, except that it does not create an output
     file, so that section of the input file is effectively ignored.

Add examples showing what this is for. Same with the rest of the page.

I don't suppose these programs evolved without examples, which are not
provided to users.