You can convert between any of the encodings for a any of the supported character sets, even the special character set called `Keyboard Layout'. However, the most useful conversions is for the Latin1 character set. You convert the current region by typing convert-character-query. It will ask you for a character set and two encodings of the character set.
(convert-character-query) Convert characters in region, query user for user character set and two encodings.
This function can be useful, not only when you want to import a file written with a different character set encodings, but also when you write TeX documents normally. You can use this function to edit the TeX document using a character set that your terminal will display correctly, and then convert the file to TeX format before you format it.