The ".rar" extension indicates a compressed archive file. These are often used to distribute large video files or PGN (Portable Game Notation) databases associated with the course.
If you are looking for specific from Part 10 of this series, English Opening For White Fitzsimons Part10 rar
: It is a flank opening that focuses on controlling the center (especially the square) without committing central pawns early. English Opening For White Fitzsimons Part10 rar