If you know how to play Forty Thieves then Rank and File will be easy for you.
Here is a summary of how Rank and File differs from Forty Thieves:
Move all cards to the eight Foundation piles, starting from the Aces and continuing up to the Kings in EACH suit.
Using two decks, each Column is dealt three cards face down and one card face up. The remaining 64 cards form the Stock.
Starting with an Ace and continuing up to the Kings, each Foundation is built UP and in the SAME SUIT.
Columns are built DOWN and in ALTERNATING COLOR.
Any number of cards may be moved from one Column to another if the build condition is met. Sequences may be split. For example, a red 6 (or group of cards headed by a red 6) may be moved to a black 7. The exposed card of each Column is always available to move to a Foundation pile or another Column.
Empty Columns may be filled with any exposed card or group of cards.
Cards from the Stock are flipped one at a time to the Discard Pile. The top card of the Discard Pile may be played to a Column or to a Foundation.
No Redeals are allowed.
Don't be too quick to play cards to Foundations. It is more important to get as many cards into the playfield as possible.
Try to build the Foundations up synchronously, or at least one set of four Foundations synchronously. Otherwise, some low ranked cards will get buried deeply in the Discard Pile, or not be immediately playable when flipped face up in Columns.
Empty Columns will play a key role in managing the game well. Use them to clear other Columns as fast as possible. Once all cards are face up, use Empty Columns to get as many Discard Pile cards into play as possible. Ideally, each play from the Discard Pile to an Empty Column should allow another movement of cards onto it, keeping at least one Column empty.
Don't forget that you may move any number of cards from Columns. This will often allow you to play cards to Foundations and open up other plays.
Finally, don't easily give up when the Stock cards have all been flipped. It will often be possible to continue playing by moving cards around Columns, freeing up plays to the Foundation.