*** The command C-x RET c (universal-coding-system-argument)
lets you specify a coding system when you read or write a file.
This command uses the minibuffer to read a coding system name.
After you exit the minibuffer, the specified coding system
is used for *the immediately following command*.
So if the immediately following command is a command to read or write a file, it uses the specified coding system for that file.
If the immediately following command does not use the coding system, then C-x RET c ultimately has no effect.
For example, C-x RET c iso-8859-1 RET C-x C-f temp RET visits the file `temp' treating it as ISO Latin-1.