You can grab a list or an object along with its fields related to other objects or lists.

Example, imagine the following structure:

Events { Title Desc Organizer { Name, Photo } }

http://yourserver/api/events?populate[Organizer][populate][0]=Photo

You will return the list of events with your organizers and inside each organizer you will have the Photo included. You can populate as many relationships or media fields as the api allows.

More Here: https://docs.strapi.io/dev-docs/api/rest/guides/understanding-populate#populate-several-levels-deep-for-specific-relations