Futsal, 5 vs 5 is what it is. 4 players and 1 keeper. Futsal is famous in many countries, it's probably the largest in Italy or Brazil. In those countries you can earn really good cash if you play professionally. Of course far away from the money 11 a side football can offer, but still very good money.
Why should you play futsal, well … it's pretty easy. If you're serious with your football you definitely should also play futsal sometimes every week. This will improve your skills in 1 vs 1 challenges and also you will know how to play a very fast game. It will require big skills to be a good futsal player. Even if you're just playing for the fun of it, I promise you that you will find futsal very funny. There is futsal clubs in most countries, they might not be to big, but they exist. Do some research in your area and I'm sure you will find something.
Just to give you an example, one of the most popular players of today … not to forget, he's also one of the best players of today, started his career in an indoor pitch playing futsal. Futsal cave has extreme skills and amazing tricks. He took these skills and tricks to the big pitch and he became one of the best players of all time. Ronaldinho !!! There is loads of big players who started with futsal but also played regular football. If you get a good balance between them you will get all the skills needed for a big pitch, you will also get those extra skills you do not really get from only playing 11 a side.
If you just love the game I really would suggest you to join a futsal team. You will have the ball so much more then in a football game.
Some of the best futsal players would be Falcao, Vanenburg and Edje. Search those names and you will see amazing skills!
It's also very common for futsal players to do some basic football freestyle, to read more about football freestyle I would suggest you to read the following article: http://ezinearticles.com/?What-is-Football-Freestyle?&id=714660