Different pools

Lending pool, Tri-pools, liquidity pools being integrated with lending protocols, etc and many others

Different features

Stablecoin swap, integrated pools, multichain existence of CRV, lending pools and non-lending pools, etc

What are the major DeFi protocols Curve is integrated with?

Hint- Compound. Do a bit more research, you will get to know others.

How does Curve Finance improve the second layer utility of a token of a different protocol?

Do a bit more research again. You can lend in Compound, and issued with cToken, that token can be utilized in Curve Finance to earn extra rewards (specific pool), indicate those pools.

I hope it clarifies.

Thank you.