The total pool’s stake consists of all coins held by the pool. These are the pool operator’s coins and all the coins of those who delegated their coins to the pool. Based on the total stake, the pool gets a relative chance to become a slot leader and produce blocks. The network only rewards those pools that produce blocks when given the right to do so. If they do not take this chance for any reason, neither the operator nor the people that have delegated coins to the pool will receive the reward.

Note that pool operators do not come into contact with the coins. All rewards are handled by the protocol itself. Operators just set the charges (taxes) for their service when configuring the node.

At the end of each epoch, the reward is distributed to both the pool operators and those who delegate their coins. Let’s call them delegators. The pool operator's reward is paid off first and the rest is distributed to all delegators proportionally to their stake.

If you would like to learn more about the blockchain incentives mechanism read our article:

Blockchain needs a viable incentive mechanism

A decentralized public network is not only about technology. The network is maintained by people for the people…

medium.com

Rewards in epoch

Epoch rewards consist of transaction fees and ADA coins that are prepared for rewarding. Epoch in the test-net is 1 day long so the reward is paid every day. You can find relevant information in IOHK blog:

The rewards for delegating stake or operating a stake pool on the Incentivized Testnet depend upon the percentage of network participation. An approximate 3.8 million ada will be awarded per epoch. If 50 percent of the network participates, then we estimate the annual return for delegation will be approximately 7 to 8 percent but could, if network participation is lower, be as high as 13–15 percent. These figures are subject to treasury taxes and stake pool fees.