what am i missing?

in the lesson "counting captures", the video shows white taking the d5 pawn with the rook; black rock takes white rook; white bishop takes white rook. white captures 1+5, black captures +5.

Why would white not capture the pawn with the bishop first? then black takes bishop, and white takes rook. White captures 1+5, black captures +3.

What am I missing that the video takes with the rook instead of the bishop?

Some thoughts...if white takes with the bishop then black is unlikely to enter into the exchange as it would leave white a rook up, so white takes with the rook which is the most forcing line as the black rook is then attacked. White wants to exchange the rooks off the board, leave their bishop centralised and attacking f7. They will then start pushing the outside passer on a2.

I believe they take the pawn with the rook to open the possibility for the white rook taking the black rook; if white takes the pawn with the bishop, the black rook isn't threatened and therefore isn't compelled to take the piece there. I don't really know though, I don't think I would've taken the pawn if I was playing that game.

Me neither. if I was black I'd let the pawn go and keep my rook on the board.

Thanks guys. I think the setup of this board was not a very good example of showing the concept of counting captures, since there is a lot more dynamic behind this setup. As they teach 'capture with the lower piece first', this example is counter intuitive, without them explaining why they capture with the rook first.

White has to take with bishop, if he wants real winning chances (although it is far from easy). Taking with rook allows Black to swap rooks, and after that the opposite coloured bishop ending is rather easy to draw, despite white's extra pawn.

After taking with bishop, Black of course won't take at d5, but rather play ...Kf8 with decent drawing chances, but he has to fight to get the half point.

Darn it. Need to work on my end game.

I still don't see a benefit to taking the pawn. Both players have the same amount of the same pieces, so after trading, it's basically down to whoever can get their pawns to the other side of the board quicker.

@pfren - Even if white captures with the bishop, the bishop is effectively pinned specifically because the opposite colored bishop ending is drawn.  The ordinary defense of the bishop moving to protect the rook (i.e. an eventual Bc4 or Be4) will result in a trade of rooks all the same.

White will eventually need to use his king to break the deadlock, but black will bring his king into the game, too, and it's not clear to me which king will win the race to threaten/protect d5.  Black will play Kf8 immediately after Bxd5.

To me, it's still a question whether white wants to capture d5 at all.  Even Bxd5 deactivates white's rook and bishop after Kf8, while leaving the black bishop mobile.  The rule of thumb I was taught was that piece activity in the endgame is worth a whole pawn, so I'm wondering whether a move like a4 might be better, especially since black can't currently blockade a5 without first deactivating his own rook, and advancing the d-pawn (which black seems to have to do to save it) further adds to the white bishop's mobility while restricting black's own.  Am I wrong to think this?

@KieMoff92 - Apologies for going into such depth on a beginners' thread (it is a fascinating position for a mid-level player like me).

Before the pandemic hit, I gave free lessons to whoever wanted them at my local club.  The topics I usually hit were (1) a full explanation of all the rules, (2) the basic checkmates -  King & Queen, King & Rook, and the back rank, (3) basic tactics - forks, skewers, pins, etc., and then (4) opening principles -  specifically development and control of the center.  This is what I would recommend for you to study, in that order.

If you get to that point, it should be easy enough for you and your son to grow as players together.

I myself was taught from a very young age. I obviously didn't know any specific strategies or openings when I started, but as I started to grasp the movements of the different pieces, the strategy eventually comes naturally. My advice, if you want to teach your son how to play, is to simply teach him the basics; check, checkmate, and the movements of the pieces. As he starts to move the pieces on the board, he'll start stringing little combinations with the pieces. And the more he plays, the more strategy he'll develop. If you're teaching him as well, your strategy will further simply for the fact that you're playing him. Just be patient with it, stick to it, and you''ll both be really good in short time.