Chess tactics and strategy are incredibly complicated, to the point where even a computer can't work out the best strategy in every situation. There are literally millions of possibilities, making it impossible to evaluate them all.
For this reason, chess strategy has been getting gradually more advanced through the ages, as masters of the time write books about their strategies and influence the next generation of players. This also means that observing a particular player's strategies can make it easier to work out how to beat them, regardless of how much you know about chess itself.
While advanced chess strategy and tactics would take years or even a lifetime to learn (it is, in fact, pretty much impossible to learn it all), we can lay out two basic moves here, just to get you started.
To begin with, pretty much the most common move in any game of chess is to pin the other player's pieces. Pinning is when you use one of your pieces to stop the other player from moving one of theirs, as doing so would allow you to take an important piece such as a rook or a queen. A skilled chess player can easily stop almost all your pieces from moving anywhere, effectively controlling your side of the board as well as their own.
A skewer is pretty much the same move as a pin, only the other way around: the more important piece is the one in front, not the one behind. It appears that you are moving your piece into the line of fire, but in reality they are covered. If your opponent takes your piece, they will lose their important piece to your covering piece in the next move, but if they don't take it, then your piece is in a position to take them. This forces them to move their important piece out of the way, allowing you to take the weaker one behind.
