There is a huge difference between match fixing and betting. Betting is legal in many countries while match fixing is illegal everywhere on the planet.
Let's have a look at betting first. Betting which is legal in many countries is kind of profession as well. People guess the match results and get money for that. There are agencies where one can bet. Betting is popular online today as well. Websites like betfair.com are one of the best ones for betting. There are different rates for different teams and results. Usually the price is high for weaker teams. For example if India is playing Zimbabwe in a cricket match and you place a bet of 100 rupees for India, you might get only 200 when India wins but if you place a bet on Zimbabwe and they won, you are likely to get 8-10 times more money that you placed. It varies place to place.
Now let's talk about match fixing. Match fixing is done by players by accepting money from gamblers. Some big gamblers who place bets of millions, contact players to change the result of the game somehow and in return they offer big sum to the players. Let's understand it by an example. Suppose you placed a bet of one million on an India vs Pakistan match. The rate is 5 for Pakistan which means you will get 5 times more money than the amount you placed. The rate on India is lower than Pakistan so obviously you will love it when Pakistan wins. So instead of trying your luck, you approach some Indian players and offer them money to play poorly. If they agreed, that means the result of the match is fixed and that is called match fixing. There is a term spot fixing where the bet is placed on a particular over or session of the game. For example the players signal the bookies that that next ball will be a wide so bookies place a bet for wide.
Note: This post is only to educate about fixing. It should not be used to motivate one for such criminal act. Thanks