How to share files over http between two devices on a local network?

Hello everyone,

I'm not sure if this is the right place to ask, sorry it it's considered spam. but I've seen a couple of apps on android that takes a file and gives me an IP address, which I can open for example from my laptop and I find the file. I just would like to know the concept behind this. just a hint and I'll Google more. I really have tried Google with no luck.

so, just a hint to help me Google it. how is it implemented, I know it uses http. but how does it upload it or link it to an ip like 192.168.1.103:9999.

thanks in advance.