You will often see characters like “^@” and “^M” in files opened by vim, but it’s not well documented how to find what they actually mean.
These are called “digraphs” and, fortunately, the full list of these are available in the vim documentation.
To insert digraphs, you can use
CTRL+K in insert mode and the two-letter alias for the digraph.
CTRL+I will let you insert a literal character (e.g. a tab if you have those turned off).
CTRL+V will insert a character by numeric value for example
CTRL+V x 41 will insert a capital ‘A’.
These commands can be particularly useful in substitutions for junk characters, but if you need to type foreign characters it can be easier to
set digraph and use backspace to add the accent to a character you just typed.