Some networks set a minimum amount required to run a validator directly — Ethereum's is 32 ETH. Staking pools solve this by combining many smaller depositors' funds into one validator-sized stake, then distributing the resulting rewards back proportionally, minus a pool fee.
Pools can be operated by centralized exchanges, by non-custodial protocols (liquid staking falls into this category), or by community-run cooperatives. The key questions for evaluating any pool are the same regardless of structure: what fee does it charge, how transparent is it about validator performance and slashing history, and what happens to your funds if the pool operator disappears or acts maliciously.
Pooled staking is what makes staking accessible to holders with small balances, and it's the model behind the large majority of retail staking activity today, whether through an exchange's 'Earn' product or a DeFi liquid staking protocol.