The explore feed on Instagram is made up of recommendations of photos and videos that the algorithm finds for you, based on assumptions of your interests.
How the explore feed works:
The algorithm will base what you see on the explore page by looking at the content you already like, and what other people with similar interests to you also like.
So say you are a big fan of a creator called carl [see diagram above] you like all of carl's posts, and engage with him often. Carl owns a bakery account, and bakery is something both you, and Carl's other followers all have an interest in.
Let's say a majority of carl's followers also follow and like the content of tow other bakery creators, Jeff, and cat. The algorithm will put two and two together, and assume if you like carl's account, and you also like bakery, then there's a high chance you'll like Jeff and cat's posts too, so these will be pushed to your explore page!
This process is repeated to make up a photo 'set' - this will consist of 1000s of photos Instagram *thinks* you will be interested in
These will then be ordered by how likely Instagram thinks you are to be interested in each post, based again on different 'signals'