The Photos app on the iPhone is where pictures, videos, and screenshots are saved in the camera roll.
When you open the app, you will be able to find all your photos organized by years, months, or days with dates accompanying every single photo in the "Library" option, or if you click on all photos, it will show you all of your camera roll with the pictures, videos, and screenshots organized in chronological order.
You can then press the "Select" button to edit, forward, or move any photo of your choice. If you press on the three little dots situated at the top right corner of your screen next to "Select" you will be able to zoom in and out, filter your library by selecting "Favorites", "Edited" "Photos", "Videos", or "Shared with You". If you click on "Show Map" it will show you where exactly on the map of the world your photo or video was taken.
If you select the "For You" option at the bottom of the page, it will show you your memories in a slideshow with music, and if you scroll down, it will show you all of the pictures and videos that have been shared with you through text messages from others.
If you select the "Albums" option, you will be able to see all of your categories including albums that you created, your favorite pictures (those that you hearted), and your most recent pictures.
Finally, when you select the "Search" option, it will take you to a search bar where you can type in specific descriptions of the photo you are trying to find, including people and places. If you scroll down it will give you some suggestions on how to find the photos that you want.