The mining reward for a completed block is awarded to that particular miner who found/confirmed the last hash. All the others who helped to fill the block in question, would get NOTHING.
In order to reach a more fair rewards distribution system, mining pools were formed. A mining pool brings multiple miners together (can be 100s or even more of them) and whoever from the pool finds the last share and get's the block reward, it get's shared among all the members of the pool, based on how much they contributed to the mining process.
The higher hashing power you dedicate to the pool, the higher % of the reward you would receive. The pools also take certain % to compensate for the costs involved with running the pool and it also serves as a source of income for those who run the pools.