Puzzles 4

 In Endgame stage the rook must be active, It is powerful if it is in the 7th and 8th rank. We must occupy open files for the rook so it can control many squares at the time. It is good at supporting pawns to promotion.

Let's condider this Example:

The rook occupy the B and D file and manuever it's rook to promote the pawn in the 8th rank.