The key to the staking concept can be wrapped just by one sentence: "Make cryptocurrencies profitable but continue to own them."
Staking is a form in which owner lock their crypto asset within a set period of time. What makes cryptocurrencies increasingly popular is that their value always has the potential to increase. Therefore, for some cryptocurrencies with optimistic values, owners can use them as idle capital to make a profit - which is usually as the staking rewards (depending on the blockchain the owner wants to stake).
In some respects, staking seems quite similar to the bank deposit model; however, there is a significant gap between these two models, emphasizing the complexity surrounding how staking works. For example, any recognized fiat currency can be deposited, but not all cryptocurrencies can be staked.