All Online Casinos use Random Number Generators (termed RNG) to determine the outcome of many casino games (slot machines, dice, cards etc.)
There are two types of RNG: 1. Pseudorandom numbers (more predictable); and 2. Genuine random numbers.
About RNG 1 - The Pseudorandum
Pseudorandom numbers may present you with blackjack game patterns which may be predictable, even though you haven't figured out the algorithm.
About RNG 2 - The Genuine Random
Genuine random numbers are predictable sequences that can be used both to the casino's advantage (we are not suggesting that the casinos cheat) and also to the players to gain an edge with accurate prediction information (assuming that you, the player, can figure out the algorithm and thus the sequence of events).
If you are familiar with computer algorithm, you could predict the sequence of the RNG numbers and thus gain a greater edge over the online casino.
Practice at online casinos that offer you free unlimited play so that you can figure out the type of random number generators they are using. It is important though, that when you convert from Free Play to playing with and for real money, you make sure that the real money game has the same peculiarities as the free game.