At some point in time, nearly every nation in the world is technically in the running to win the World Cup. After a couple of years of qualifiers, though, only 32 head to the selected site to actually contest the tournament. A month later, two remain.
Argentina have gotten here through a stingy defense and Leo Messi. They tend to sit deep on the pitch and invite pressure up to the edge of their penalty area, at which point their two banks of defenders make finding a way through incredibly difficult. If the ball is surrendered, the Argentines look to break quickly into the space in front of them while the opponent is still recovering. Obviously, having the best player in the tournament, if not the world, helps spackle over the cracks in this approach.
Germany has taken the opposite approach, pushing the defensive line high up the field to try to regain possession while still in the attacking half of the pitch. This has worked wonderfully for them, and their midfield has snapped into place with both Sami Khedira and Bastian Schweinsteiger now fit enough to push Phillip Lahm to his natural right back position. Crucial for Germany's overall success has been keeper Manuel Neuer's willingness to sweep up behind the defense. The German backs are not blessed with speed, but Neuer has covered a lot of miles making sure there isn't empty space behind them for opponents to play into.
This game will be won and lost in two places. The first is the center of the park. Germany's midfield has been rampant in the knockout stages, and they need that to continue for their plan to be successful. Any Sunday league player can pick out a damaging ball behind Germany's back line if given enough time, so Germany has to be able to put pressure on Argentina's central midfielders before they have time to look up and play a long ball. Ball pressure and retention in the midfield keep the German team out of trouble at the back and doing damage going forward.
The other is the Argentine right wing, where Leo Messi likes to receive the ball. German right back Benedikt
Cumberbatch Howedes is actually a center back playing out of position, and he figures to have his hands full with Messi out there. Germany will have to rotate help his way, but they need to be careful not to get drawn too far into stopping Messi. The Dutch set up there side to hold him down in the semi-final. It worked in the sense that he did not score, but it did not work in the sense that the game was tight and dull and The Netherlands lost anyway.
There it is: four paragraphs to get you prepped for the game. You can find deeper analysis by the brilliant Michael Cox here, but it's pretty much going to be what I said plus some window dressing.