What is current do it really exists why does it flow opposite to the flow of electron and also why from positive terminal to negative terminal does current really flow or is all thing done by electron

The opposite flow of electron is called. The word current is not an object, it is just a name of opposite flow of electron. Because electron is a negatively charged particle. So obviously the opposite flow of electron will be positive, which is known as current. (if there would have a possibility to flow of protons then we would called the current direction as same as the protons for it's positive charge.).

The negative terminal and the positive terminal means the more abundance of electrons In negative terminal with respect to positive terminal. And because of the potential difference of electrons between negative and positive terminal or the number difference of electrons between negative and positive terminal, the electrons will flow from negative to positive terminal. And we know that opposite direction of electron flow is called current, so the current will flow from positive to negative terminal.

And the only particle of conductor which is in a free state is electron. Only electron can move through out the conductor. So the current is the only reason of the opposite direction of electron.