I have a short simple answer that I have been giving folks and in general they seem to understand it right away.
STEEM is hard to earn. You have to write a lot of articles, or spend a lot of time voting, to earn very much at all. Sometimes a post earns nothing, sometimes it earns a little, some posts actually do earn a lot. But in general it is hard to earn STEEM. It's so hard that I might not feel like doing it. But I want some. If you have some, I might trade you some BitCoins or some USD$ for it. That's where the money comes from. Or I might offer you goods or services for it. That's where the value comes from.
Writing articles is like mining for gold. You go down in the hole and dig up a bucket of dirt. It's hard to dig in the dark hole. You bring the bucket of dirt out and see if there's any gold in it. Sometimes there's none, sometimes there's a little and sometimes there's a lot. When you get some, you can bring it into town and there's guys there who want gold, but who don't want to dig for it. They will pay you in cash or in goods and services. That's why gold is valuable. No other reason. Just like STEEM.
To improve the community and the value of STEEM,
Post and vote for creative, original work that you like.
Please try my Future History stories - Enmity