not trying to be offensive payne but are you by any chance an older person?

an app is an application for short. smartphones have apps.

its like a photo log of whatever you want to show. some people take pics of their pets. a lot of people take pics of nature. or just anything.

i say theres people with mental health issues on there because some peoples pics are all about what they go through.
warning though - some pics are triggering - ive seen some people take pics of their self harm areas.

its hard to explain if you dont even know what an app is.