By contributing to the Cardano ADA network, one can receive rewards as compensation. This is not like investing to make a profit from buying and selling, but more like investing in a trust fund.
Cardano ADA holders can contribute to building the Cardano network, maintaining security protocols, decentralization, and governance by staking (delegating) their ADA and earn rewards in return.
You can contribute by delegating to a pool operator, who will monitor the network and verify transactions on your behalf. (This is due to the Proof of Stake (PoS) mechanism.)
The mechanism adopted by Bitcoin and other cryptocurrencies is Proof of Work (PoW), where rewards are received by mining. However, Cardano uses PoS, so if you hold Cardano ADA, you can contribute to the network by choosing a pool to delegate. Then you can earn rewards.
Therefore, you need to choose a pool that is trustworthy and well-operated, as well as decide which pool is best to delegate to.
In terms of receiving rewards, payments are made every epoch. An epoch lasts for 5 days. For example, suppose you delegated your ADA on epoch 261. In that case, your delegation will be effective from epoch 263, 2 epochs after delegation.
The first reward will be generated 1 epoch after delegation, which means that if you joined at epoch 261, your first reward will be received on epoch 264.
Once you delegate, rewards will be paid out between the 11th and 15th day after delegation. After that, as long as you don’t unstake, rewards will be generated every epoch, which is every 5 days.