Wittgenstein believed that every word we speak is all part of a language game. For Wittgenstein language games were similar to an inside joke. You would only get the joke if you were in on the joke. This is similar to language, you will only understand the language being used if you are familiar with the language. That is why Wittgenstein believes that Religious language is meaningful, but only to the religious believers. they are all part of a group that regularly use that language, which has a deep meaning to them. Non-believers would not think that religious language is meaningful, because we are not involved in that 'game'. Wittgenstein refers to words as 'tools' because we use them to build our houses.
Words have meaning only in the context of a game. Whilst watching a football (soccer) match, this philosophical idea occurred to Wittgenstein. If a person with no prior knowledge of football is watching a game, to him it will seem very random and meaningless. For it to take meaning, he must first understand the rules of the game: there are two opposing sides, each has eleven players, each is trying to score against the other by putting the ball in the opposite net etc. Once he understands the overall context of the game then the men running around chasing a ball no longer seem mad but have meaning in the game.
So too, concluded Wittgenstein, is it with language. If one does not understand the context of the language and the rules that are imposed upon the specific discourse, then essentially, one cannot understand the words in their truest form. He acknowledged that people who understand the rules of one game (i.e. football) can find similarities in other games (i.e. Rugby) but essentially, these games are inherently different and thus to understand fully, one must understand the specific rules of that game and its differences from other games.
What Wittgenstein was saying was that language only has meaning in its specific context. When taken out of that context and put into a different one, it may not mean the same thing. Wittgenstein was warning us against prescriptivism and being too stuck in one way of thinking. Wittgenstein thought that one could not stand outside a game and legislate about it or attempt to impose the rules of another game - you cannot play basketball as if it's football! So too, he said that a player of one game could not criticize the player of another, without first learning the rules and entering into the game (i.e. people cannot criticize others' use of language without first understanding their full context and intended meaning).