All 3 of them represent the end of a line. But...
\r (Carriage Return) → moves the cursor to the beginning of the line without advancing to the next line
\n (Line Feed) → moves the cursor down to the next line without returning to the beginning of the line — In a *nix environment \n moves to the beginning of the line.
\r\n (End Of Line) → a combination of \r and \n