Bitcoin is a digital currency created in 2009, by a programer with the pseudonym Satoshi Nakamoto. It offers the promise of lower transaction fees, than traditional online payments and unlike government issued currencies, it is operated by decentralized authority. It has become a gold standard of currency, a digital gold if you will! 

Cardano is the first, third generation coin that has been through academically peer review, and differs from bitcoin and ETH by being proof of stake instead of a proof of work coin. Both ETH and Cardano differ from bitcoin with being able to run smart contracts on their blockchain. Cardano also seeks to solve many problems that The prior generation coins could not solve.

Security, Scaleability, Governance as well as being more Decentralized than bitcoin. 

Staking is the process of actively participating in transaction validation (similar to mining) on a proof-of-stake (PoS) blockchain. On these blockchains, anyone with a minimum-required balance of a specific cryptocurrency can validate transactions and earn Staking rewards.

On the Cardano network you can stake as little as 5 ada. 

A snapshot in time occurs roughly every 5 days, called an Epoch. After a pool is chosen and a delegation is made, delegation is "active" after the next snapshot (5 days). If blocks are produced in this Epoch, you will receive rewards after 2 more Epochs. there is a min of 15 days and up to 20 days to receive rewards depending on what day in Epoch delegation has been made