Novice Needs Help

Capturing the bishop was better because after you castled black can capture your d pawn for free.

"To take is a mistake" is generally good advice for when you're unsure what to do, but as a beginner the most important thing you can do is not lose pieces for free.

Actually I made a topic about this recently, you might find it useful:

https://www.chess.com/forum/view/for-beginners/the-most-important-concept-for-all-beginners

Gents.   Thanks.  The fog is starting to lift.

think of exchanging as removing a defender of something, for both sides. we know that every piece controls squares and/or defends another piece. then see whether that something left undefended can be captured or, in case of a square, occupied. do this for your side and the opponent. then you should be able to decide whether it is worth exchanging on any given turn or not. hopefully this makes sense.

6.Be7+ is not available, maybe you meant 8.Bxd7+

Also it exchanges off your opponents good bishop. Their central pawn structure is on dark squares and their DSB has terrible prospects. It weakens d5 which is a terrific hole for your knight.