There is some subtly to the game of poker, that most people cannot accomplish.Cards are luck. Admit it.
Myself I do not play. If I did, then this is how I have to do it in order to win.
Suppose it is that Texas Hold'em I think they call it, where you are dealt two cards and three are face up.
1. You look at your two hold cards, calculate the face up common cards and deduce your chances of you hand improving, on the next two cards.
2. You have to read your opponent. First is he/she/zir bluffing. If not, given the betting patterns, what do you think he has and what are the percentages of him improving it on the next two cards.
There is a real subtly there, because if you have 2 pair or three of a kind, you are in a very strong position, and in poker lore, do not check - raise when you got a hand. If you are looking for another card to make that straight or a flush, you probably are not going all in, only if you make it then you go all in. Unless you really want to gamble.
3. You're looking at the size of the pot. If you have x% of winning in your estimation, but the pot is x+more than your percentage of winning, you have to take that overlay all the time.
In short, in poker you are always making a mathematical calculation. But that is not enough, as you have to make that mathematical calculation for your opponent too. Then relate that to the size of the pot, to decide if that is a good bet or not.
Then ... is he bluffing ...