A simple position to explore. 1.e4 e5
With white's first move white threaten to setup the classical center 2.d4
So what's so powerful about the classical center. IF black develop his knights to f6 and c6 without hindering the advance of these pawns then they could advance and drive them away from the center.
All strong moves usally have more than one good point, in chess is almost always good to be effiecent to get the most out of a single move. So White now has open a line for his light square bishop to be develop after it comes into play white will be one move closer to castling.
1..e5 black's first move prevents white from setuping up the classical center.
If 2.d4 exd4 3.Qxd4 Nc6 Black has destroy the White's center and now is gaining a tempo by attacking the Queen this is known as the Center Game.
Again all strong moves have more than one point. Like white's last move this has open a line for Black's dark square bishop.
Now that we understand why the first two moves were played we too develop a plan of action. Since we are still in the opening we would like to get are forces into the action and gain a better foothold in the center.
1st Question to always ask is are opponent threatening anything? The answer is here no.
2nd Question what problems in are position do we need to solve? We need to develop are forces. The knights have good squares to go to f3 and c3. The bishop can reach a powerful diagonal by going to c4 that eyes the f7 pawn. It is unclear where the queen belongs. There are no open lines for are rooks. The dark square bishop needs a pawn to be push in order for it to get into the game. The king is still in the center so It would be nice to have the option to castle for safety.
3rd Question: Do we threatening anything? Answer here no.
So these question help us get closer to a general plan that we will conduct for the next few moves. The point of why we want to develope a plan is what if are opponent does nothing or avoids a theoretical continuation if we have develop a logical plan we will not be lost.
4th Question:Who is better in the center? Answer here even.
How would we be better: If we play d4 or f4 to disloge the pawn on e5 which is helping black fight for the center at the same time these pawn breaks will help open a line for our rooks.
So we know that are plan has to include one of these advances.
The benefits of d4: increases the scope of our queen and opens a line for the dark square bishop. And will allow a rook to be develop along a central file.
Pitfalls of d4: exd4 will leave the e-pawn expose to attacks on the newly open half-open file for black.
The benefits of f4:threatens to gain central pawn majority. When we castle king side are rook will be develope as well in one move.
Pitfalls of f4: exf4 will leave the e-pawn expose to attacks on the newly open half-open file for black. f4 does not help or develop a new piece. This move risk expose the king along a potential dangerous diagonal h4-e1.
f4 is the riskier move: but it does offer benefits that d4 can't. The f4 plan is use in the following openings from this position: King's Gambit, Bishop Opening, Vienna Game.
So we decide not to take the risk and play it safe with d4.
If we know opening theory we can save some time. From Here openings that use this plan are: Center Game, Scotch Game, italian Game, Ponzziani, Ruy Lopez, Petrov.
The four knights is a example of white delaying his decision of either f4 or d4 inorder to gain more information on which would be the better advance.