How do blackjack simulations work?
Any simulation is based upon a set of assumptions - the simplest assumption in blackjack is that any card drawn will be of value 10 (i.e., 10, J, Q, K). You run your simulation with that assumption, which drives your strategy (e.g., the simplest being hit if you have 11 or less, stand if you don't). Run a million hands and see how you fared.

If you're not in the hole by a lot, great. Your strategy works reasonably well, and you could stop there if you wanted. If you are down a lot of money, then you need to start modifying your strategy until you find one that works well (enough). And, without some guiding principles based on probability and such, to do that you really do need to test just about every possible strategy you can think of (within reason). 

The beauty of this is that computers are really good at running millions and billions of hands, and so running all these simulations is not as bad as it may sound (I would expect a well-written program to be able to simulate 1 million hands in a matter of minutes, so you can run hundreds or thousands of different iterations in a day). If you can apply some math and statistics, you can likely reduce the number of modifications you need to run.

So you start out by modifying your bet (double down if you have 11, for instance), or your hit/stand rules (split Aces), or your assumptions (hit on 12 if the dealer shows 10, because even though you're likely to draw a 10 there's a possibility you won't). The key is to only modify one element at a time. At the end of each run, compare your final chip count. Find the run with the highest and there you go. You could then start to combine some of your highest scoring modifications and see how the combination fairs (double down if you have 10 or 11, for example).

In the end you wind up with a set of rules for how the player should bet and play, to maximize their winnings / minimize their losses.

This is a type of simulation called Monte Carlo simulation, in that it uses a random hand to simulate the play. Run enough times, the randomness can lead to a deterministic answer. In fact, each time you run your simulation, you are trying to calculate the house advantage - if you start with $100 and wind up with $98, the house has a 2% advantage (or something like that). The closer you get to simulating perfect play, the closer you get to calculating the true house advantage.