King and pawn endings: what is the opposition?

The opposition is the key to almost every king and pawn ending.

The kings stand on the same file with one square between them. Whoever does not have to move "has the opposition" — the other king must give way.

Questions for discussion:

• With White to move here, is it a win or a draw? What about Black to move?
• When should White play e2-e4 — immediately, or after improving the king?

Post your answers with a line of moves. Bonus points for a position from your own games where the opposition decided the result! ♚