How does the global economy function when no country is economically self-sufficient?

For example no country produces 100% of anything. Even the US can't supply everything it needs without importing anything. So how does this work? If everyone is importing all their necessary goods, what is the point of exporting anything? Shouldn't we just build everything we need? What prevents the world from just going into a global depression or collapse if everyone is counting on importing everything they need to survive? I'm trying to understand how this works, or why countries even bother exporting anything?<br><br>Any explanation would be greatly appreciated, thanks!