Some protists use photosynthesis to obtain nutrients but some engulf other cells.
Annelid worms get their nutrients by digesting food that they eat. They eat poop, dead grass, and some bacteria.
Insects get nutrients by eating plants, other insects, and fruit. the food then goes into the digestive system and is digested.
Amphibians eat other organs to get the nutrients they need. Some, when in the larval stage, eat algae.
Mammals also eat other organisms, some eat meat some eat plants. The type of organisms they eat depends on their strength nutritional needs, and other things.