Poker is a game of betting and hand ranking. The game has many variants, some more serious than others (like straight poker) and there are also home games only variants that involve passing cards between players or making low hands instead of high ones (although those can still be quite serious). Despite the variation in poker games there are certain principles that apply to most of them.
The most important aspect of poker is determining what hand is winning. Of course this is easier said than done but there are a number of factors that can influence your chances. For example the strength of your pocket cards is very hard to conceal from your opponents. For example if you hold pocket kings and the flop comes A-8-5 then people are likely to expect you have three-of-a-kind and will be much more likely to call your raise than they would have if the flop came an unsuitable card like 5 or 2 for example).
Position at the table is very important too. It is best to act last because this will give you more information on your opponent’s actions and allow you to make more accurate value bets. Also you should try and identify conservative players from aggressive ones because they are less likely to lose money and can be bluffed into folding more easily.