Understanding how content is packaged or delivered

Hey everyone, I have a noob question. I am trying to understand if/how external objects are loaded into a game. Take sprites or pre-rendered images for example. If I am building a iOS app that uses the unreal engine, are all of the objects included in a bundle that is then published? Are there ever any scenarios where content is fetched using some sort of just-in-time event, or perhaps streamed in?

If so how is this done? Does Unreal allow for standard methods like HTTP requests? Or is there a proprietary way to fetch/load content?

Thanks in advance for any help!