White plans to bring the d5-pawn under attack from the flank, or entice it to advance to d4 and undermine it later. White will couple this plan with a kingside fianchetto (g3 and Bg2) to create pressure on the light squares in the center.
The Reti Move By Move should be what youre looking for:https://www.everymanchess.com/reti-move-by-move
I am looking for a book (or online resource) about the Reti opening, which outlines its basic characteristics, variations and strategies, but without neither being too general or getting into great length. There are fine books about the Reti out there for sure, but I need one that sums the general ideas and variations up, before starting to get into details and games.