Looking for help in developing idea

I have an idea involving the use of an app. What I am trying to get to is ,that an individual can place an item on the app for other people to be able to search or browse for it. The thing is I have no experience what so ever with this medium bar using them. So what am looking for and what about database building ,storage etc. I know this is a bit vague but Just need someone to point me in the right direction.
Needs to be for IOS and Android and have know idea about different coding and tech words used