How to establish a repertoire of openings?

I don't mean in the conventional sense -- i.e., 'how should I study chess openings and become good enough at them for them to be in my arsenal'. What I mean by my question is that I am confused by how one plays certain openings due to the moves of the opponent. I'll try to explain what I mean. For example, the Sicilian defense -- I see that every famous chess player played a version of the Sicilian -- but no just on black, on white as well. This doesn't seem to make sense to me because I thought that the Sicilian was based on black's move of d4, no by anything that white plays. So, how can one have the Sicilian as white as a main facet of their repertoire? Or do I not understand how openings work? Is there a way for me to play the Sicilian as white if black does not engage in it? For example, if he plays the Dutch. 

And something more concerning to me is this: should I play my opening as white near-regardless of what black plays? Not in the brainless sense (i.e., continually playing the main line and getting check mated instead of countering in any way), but in that I should establish the King's Indian Attack even if he plays something such as d4 -- ignoring his wish to play the Sicilian and instead establishing the pace from my end. Or am I forced to meet d4? 

And as black, if my opponent opts, for example, to play the Ruy Lopez, might I still play the Dutch indifferent to his opening and attack the king side, or am I forced to meet his bishop and continue to play the main lines of the Ruy Lopez?

I know this is quite a lot of information, but this openings stuff is tremendously difficult to understand.

I'll appreciate any responses.

Sicillian: (black plays)

Spanish: (black plays and white)

KIA (white)

ur knowledge of openings is clearly flawed???

You sound slightly confused by things. My advice would be to forget about trying to remember specific openings, their names etc for now and just play what you think is the best move right from the start of the game. But to try to answer some of your questions...1.e4 c5 is a Sicilian defence. So black has chosen that it will be a Sicilian by going c5. From this point both players are playing a Sicilian opening (of which there are many variations). To be a top player who plays 1.e4 with white you must be able to play Sicilian positions well because it is a popular choice for black. The Dutch is 1.d4 f5. Again it is black who chooses that it will be a Dutch by playing f5 against d4 by white. The Ruy Lopez is 1.e4 e5 2.Nf3 Nc6 3.Bb5. So you cannot play the Dutch if white goes 1.e4. But as I said at the beginning all of this is not tremendously important. What is important is understanding what your opponent is trying to do, seeing what you yourself can do, and not losing your pawns and pieces. 

If White plays 1 e4 regularly, it is quite likely that, from time to time, the reply will be 1...c5 and a Sicilian will result. However, White is not able to force the game to be a Sicilian. It might be helpful to do some reading in Discovering Chess Openings by GM John Emms (2006).
https://web.archive.org/web/20140627114655/http://www.chesscafe.com/text/hansen91.pdf

The things are quite simple: as white you make your first move (e.g., 1.e4) and now black will tell you how the game will go on. He will play perhaps ...c5, ...d5, ...c6, ...e6, ...e5, and some other moves too. You have to have at least an idea how to react to these answers. How do you do this? There are two main approaches. Some people say you don't have to know everything, just opening principles (don't make too many pawn-moves in the opening, don't move your pieces twice in the opening if not needed, etc). Other people prefers a more concrete approach. They will take a repertoire book and begin to learn the lines suggested by the author. 

What is the best approach? I don't know. For me playing only using opening principles will not work, as some openings are so tricky that you have to play rather concrete moves to survive the opening phase. If you are interested in some repertoire books, let me know, I can give you some suggestions.

I am not exactly an expert on this sort of thing, but my understanding is that, if one starts with 1 e4, some moves (like 1...e6) lend themselves to a King's Indian Attack while others (like 1...d5) do not. I think the details are different if one starts with 1 Nf3, but the basic idea is still true that it is not always a good idea to seek the KIA. If I remember correctly, there is some detail about possible continuations after 1 Nf3 in GM Seirawan's 1999 book, Winning Chess Openings.

https://web.archive.org/web/20140627132508/http://www.chesscafe.com/text/hansen173.pdf

After 1 e4, it does not make sense for Black to go for a Dutch (with ...f5). Nevertheless, White is unable to force a Ruy Lopez. For example, after 1 e4 c6 2 Nf3 d5 3 Bb5, White would have serious positional weaknesses.