So im new in Wizard 101, and im really trying to decide one school , im with balance,life or death.
But can someone answer me something ... im just suppose to chose one school and just buy power from one school or like from more then 1 to create combos?
You should read the guides furnished on this site or on fansites like Wizard101 Central or the Wizard101 Wikia.
A short answer to your question is that once you choose a school, you get all spells from that school for free, provided that you are the proper level and/or do the required quests to earn them.
Spells from other schools cost what are called "Training Points". You earn points at various levels (1, 4, 8, 12, 16, 20, 25, 30, 35, 40, 45, and 50), and by completing each of Prospector Zeke's quests in the various worlds. These can be spent learning spells from other schools.
Spells are not "combined", per se, on a given turn. Each spell is used individually on a given turn. However, you can stack enhancements (i.e. blades and traps) on successive turns so that the attack spell you cast causes more damage.
I CAN help you, my friend. As colagada said, you get spells from your schools for free, and then, we wizards have a system. We pick "second schools." First, you pick your school. If you pick life, you probably don't want death as your second school, because they're opposites. And death is the opposite of balance, etc. Life is cool because you have healing spells. Death spells are cool because there are skeletons and vampires and bats..I think you get it. Balance is probably the coolest of the three because you have wards and charms of all sorts. It also has Hydra, which is probably the highest damage spell in the school system besides Stormzilla.
Hope I helped! Your Friend, Alexis Frostcrafter, Lvl. 28 Thaumaturge (Ice)