The stuff you sold to get money, like USD or Euros or Trade Dollars, was valuable. Someone wanted it. They gained by getting it. Now you've got this "money", but you can't eat it, ride in it, and probably not even fondle it if it is in the "bank". The stuff you will buy with it is valuable though. That's why you would trade what you had, via money, to get something you want even more.
Let's go over that again. The money itself is worthless. It's only what it will buy that is valuable. Money is only a stepping stone to split a barter transaction into two parts so the person who wants what you have doesn't have to have what you need in order to trade with you. You can provide what you have to someone who wants it and get what you want from someone who can provide that. Money is the bridge.
Is that about as clear as mud?
It boils down to this, that money is a record, a proof of claim. You provided something and money is used as proof that you've got something coming. That's it. It doesn't matter what form the money is in, bits of paper with numbers on them, a bank's or trade exchange's records, or some jingly bits of metal with numbers on them, or something else that keeps track of the value you've got coming to you.
Money is just accounting for value delivered. It's to keep track. It's information about what you got coming. That information can be stored on paper, wooden sticks, piles of pebbles, computer records, or in our heads. In our heads isn't a very good idea, so scratch that, it makes for arguments. Keep a copy in your head if you like, but don't expect everyone else to be satisfied with just that.