You're not wrong, except the part where the money becomes more real once you sell the stock. All assets are like this -- if you lasso an asteroid that contains $45 umptillion of gold, you won't be able to sell it for $45 umptillion because you'll crash the gold market. Money has the same problem -- when the money supply grows, everyone has less money per money, which we call inflation.

I don’t have economics background and think the same way as you do.

They just create money out of thin air.

I have a bachelors in economics and your pretty close except you’ve got realize that all money is like this. If you’ve got a us greenback in your pocket and if I decide it worthless to me, and you want something from me then all you’ve got is a small piece of art.
All value is just agreements between people and money is just a method of keeping track of favours owed that we worked out thousands of years ago. In the example of a stock, all a stock is, is an agreement between the company that issues it and its holder, that the company will do you a favour (give you some money, a dividend) some time in the future, and keep doing it every time they have some extra favours to hand out.
I may decide that the promise of those future favours are worth doing a lot of favours right now or only a few.
Right now everyone who buys and sells stocks doesn’t think a lot of companies aren’t going to be able to a lot of favours in the future so the value in the stock market has gone down. But that doesn’t mean a trillion dollars has disappeared it just means that the offer of money is lower

To be fair the very idea of value of money is "imaginary". Even a bank note is nothing more than a promise.

The value of a stock is derived from the trust that someone will trade you for it. If the trust goes away, so does the value.

Similarly, the value of a bank note is derived from the trust that someone will trade you for it. If the trust in a bank (bank run) or government (scarce money supply, solvency) or economy goes away, so too will the value of money, i.e. inflation.

Even comodities and tangible goods have "imaginary" value, because these things can be under or over produced, which in turn changes how likely someone might want your good.

That being said, the degree of imagination needed to trust the value of trade varies, and stocks are definitely close to the top of the imagination tree.

You don't need a business degree to know you are correct here. Someone whom may or may not be I has one though, and you are correct.