You can use fprintf on a file just like you might on a console with printf. For example to keep track of game wins, losses and ties you might write

/* saves wins, losses and, ties */
void savewlt(FILE *fout, int wins, int losses, int ties)
{
    fprintf(fout, "Wins: %d\\nTies: %d\\nLosses: %d\\n", wins, ties, losses);
}

A side note: Some systems (infamously, Windows) do not use what most programmers would call “normal” line endings. While UNIX-like systems use \n to terminate lines, Windows uses a pair of characters: \r (carriage return) and \n (line feed). This sequence is commonly called CRLF. However, whenever using C, you do not need to worry about these highly platform-dependent details. A C compiler is required to convert every instance of \n to the correct platform line ending. So a Windows compiler would convert \n to \r\n, but a UNIX compiler would keep it as-is.