If you have the technical knowledge and resources, you can get started staking by running validators. This will require maintaining a highly available server, active monitoring, and at least one upgrade per month. Certain protocols will have a minimum required amount of stake in order to enter the active validator set and earn rewards.
Users should first start running validators on testnets in order to understand the requirements and process of running a validator. There will be dedicated validator support and validator community channels for each protocol to get assistance and troubleshoot problems.
Most protocols have a special transaction type called delegating. This action lets users retain ownership of tokens, while those tokens can be used as stake by validators. Delegating lets users stake without giving up custody of their assets.
Delegating will be the easiest form of getting started with staking as it does not require any technical capabilities other than managing wallet private keys. Most wallets will have delegating functionality natively built into their UIs.