To look after someone or something means to take care of them and make sure they're safe, healthy, and doing well. When your parents ask an older sibling to look after you while they run errands, they're trusting that sibling to keep you safe and help if you need anything. When you look after a neighbor's cat while they're on vacation, you feed it, give it water, and make sure it stays healthy.

Looking after requires responsibility and attention. A lifeguard looks after swimmers at the pool, watching carefully to prevent accidents. A teacher looks after students on a field trip, counting heads and making sure everyone stays together. You might look after your little cousin at a family gathering, making sure they don't wander off or get into trouble.

The phrase suggests ongoing care and attention to needs. When you truly look after something, you think about what it needs and make sure those needs are met, whether that's watering plants regularly, helping a younger student with homework, or making sure your pet rabbit has fresh food and water every day.