Call: This is the betting option that the player will use when they wish to match the highest bet that is currently put out on the table. If one player bet $40, then in order to call the player would also have to bet $40. However, if one player bet $40 and another player raised $40 then the player would have to bet $80 if they wanted to execute a call action in that particular hand. Calling is one of the more important betting actions around because you can evaluate yourself as a poker player by how often you call in a particular situation compared to how often you execute another action.
Raise: When a player elects to raise, then they have decided that they want other people to put up more money rather than simply matching the bet that is currently out on the field. The raise option only appears like the call option when there is already a bet out there from another player and depending on the betting structure you have in the game, the raise amount might be different. In limit games the raise is automatically the amount of the bet for that round, whereas in pot limit games it is maximum the size of the pot once the amount to call has been taken into account. In no limit games, it is any amount that you want.
Fold: Folding is the simplest action that a player can take and if you are a tight player that tends to win at poker games, it is also going to be the action that you take the most often. It is simply refusing to put any more money into the pot and instead of continuing with the hand, getting rid of your cards and living to fight another day.
Check: A check is a specialized betting action that is only available to you when no bets have been put out in that particular betting hand. It is basically an election to not put any money out there on your own, but at the same time to keep your hand and see what the other players decide to do. If all the players in the hand check a round, then the next card is dealt without any betting having been done that round.
Bet: Bet is the other option a player gets along with the check option when there are no bets out there. It is basically the same thing as a raise, except the player is raising from nothing rather than raising a bet another player has already made.