A Knight outpost is a nice fairly central square for a Knight that the opponent cannot, or dare not, swap off or drive away. Teichmann Pegararo and Smyslov show how to use such outposts:
Even if your position looks OK, you may be worse because your opponent has the initiative. The initiative is the ability to create threats. You can't get settled and finish developing if your opponent uses the initiative well, and you won't get your position sorted out and equalise if you are constantly bothered with threats.
Here are three examples, from simple to complex:
Two from Alekhin where good beginner's opening principles are ignored, in favour of seizing the initiative. (Poindle, Wolf)
A hole in a chess position is a square in the pawn structure that cannot be defended by a pawn.
It is a square that your opponent's pieces might be able to sit in and you can't get them out. (Steinitz-Blackburne) It's like having a nail in your shoe...
A hole used like this is an outpost.(Smyslov-Rudakowsky)
Rooks sometimes sit around in corners at the start of the game, when you really want to get them working for you. To do this, you need an open (or a half-open) file.
A open file is a file without pawns. Put your Rooks on open files, or both Rooks one one open file. Control of an open file is useful in itself, and is also the route into your opponent's seventh rank (van Vliet - Znosko-Borovsky).
A minority attack is where you advance pawns on the wing where you have fewer pawns. This works if your opponent's extra pawn on that side is backward on a half-open file. The furthest square on a half-open file is an outpost for you, and if your opponent attacks your piece on that square with a nearby pawn, they may be making weaknesses. (Capablanca-Janowsky)
You see lots of minority attacks in the Queen's Gambit Orthodox Defence (Evans-Opsahl) and Sicilian Defence (Conrady-Benko, Vogt-Andersson)
Not exchanges in general: The Exchange. The Exchange is when a Bishop or Knight is swapped for a Rook. By normal chess accounting, that's a swap of 3 pawns for 5, so one player has lost the Exchange, we say, and is then an Exchange behind in material.
Losing the Exchange is enough to lose the game, as the more powerful Rook can usually create more problems than a minor piece can solve.
Usually. In an endgame without Pawns, K+R vs K+B or K+N should be a draw.