How to get better at calculation?

You cannot improve calculation with practice?

You can improve calculation with practice. Kasparov wasn't born as the best chess calculator in the world. He became that through practice and with the help of natural talent.

How does 2.Kf2 win a piece after 2...Qe7.  White is down a pawn.

Calculation is one of those things where you can do it or you can't. It's not something you can really improve on.

You cannot improve calculation with practice?

Not really, if you do it'll be miniscule compared to where you'd be with just natural talent by itself.

White won a bishop and a Knight. Black won a bishop. Therefore White won a bishop in that exchange.

This is the position i am referring to...

idk about "sharp" here

If White is in this position (about 12 moves) with 2 minutes left and questions, there are definitely multiple issues.

Whether it was a Tartakower, a QID, or something else...the big issue is the handling of the fight over the center (likely both sides, but White suffers the most now).

First, slow your roll and take your time.

You have to take the bishop if you want to win a piece in the exchanges. I didn't see that white is down a piece in the starting position. White will lose the f2 pawn. That's the least bad option.

There are no issues. He plays the time control he likes. And he plays the way he likes to play.

It's a position that a friend of mine played earlier today.

2 minutes left on the clock, I added that for illustration.

For most players 2 minutes is a short amount of time to finish the game but if you are a bullet player it is a luxury.

You're right

If he likes playing a piece down, that's the line to take.

I don't care what time control...it's bad chess. If that's a luxury, I'd rather be poor.

This is the easily winning position for White that I ended up throwing away https://www.chess.com/analysis/game/daily/340127137 in this game I played the mistake b3 (to allow the dark squared bishop to come out without getting spanked with Qxb3).

White has many advantages: castled king, three pawns in the center, two developed knights etc

Despite the uncoordinated Black position: there are several threats to White:

• Queen can capture Qxb2 not a problem with bishop on c1 but if that moves away then the Black Queen on b2 also attacks the knight on c3
• Both Black Queen and Black bishop targeting d4 pawn, black could add a 3rd attacker with c5. If Black bishop is able to play Bxd4 and I have no pieces left to recapture then my knight on c3 could be in some trouble 
• Possibility of kingside attack with ...Bg4 or a pawn storm

Better moves would have been:

• c5 - although this did not first appear to be very good since ...dxc5 puts me in a tough position as I don't want to recapture dxc5 and don't want him to capture cxd4, maybe with more puzzle practice would have spotted the Na4 Queen attack. One advantage of playing c5 is it stops Black from playing c5
• a3 - allowing b4
• h3 - the move that Chernev described as a "coffee-house move" in Logical Chess, actually a good defense here

How about this position? Black is to move.

What should Black play?

Do you derive this move via general principles, calculation or a combination of the two?

I would be afraid to lose d6 pawn, so I would play Be5 defending the pawn and interfering with the connection between the queen and bishop. Be5 forces Bh4. I would say that white has a good position despite being down the exchange because of the h4 pawn (which is a protected passer), because the bishop on b5 is really strong. It controls e8, it stops the c4 pawn break, it blocks the b file which means that the rooks can't target the b3 pawn. The other bishop will control the e7 square when white plays Bh4. White controls both e7 and e8 which means that black can't put the rooks on that file. White owns the e file. Honestly, I would rather play white here, despite being down an exchange.

This looks like a very complicated position though. So many options for both sides after only the first few initial moves which I thought could happen. I have no idea who's better or what's going on in the positions which I reached down below. However I think that black has to defend the d6 pawn first.

I found a useful video by Dan Heisman that features calculation of an endgame position 

https://m.youtube.com/watch?v=z6Bh6StWvvs&list=PLRWUHVsN-mIJNwc4cLdVmV4L1yk8vNMaM&index=1 

There is no trick, just practice it. No shortcuts to any skills

Nah, it's mostly pattern recognition and how good your "working memory" is.