what actually flows in the electric current

Electric charge. From the Wikipedia article Electric Current:

An electric current is a flow of electric charge

Negative (by convention) electric charge is carried by electrons and so a flow of electrons is also a flow of electric charge. But the negative sign of the charge means that the electric current (due to the flow of electrons) is in the opposite direction of the electron current.

If the charge on the electron had been deemed positive rather than negative, then the flows would be in the same direction.

what actually flows in the electric current

Electric charge. From the Wikipedia article Electric Current:

An electric current is a flow of electric charge

Negative (by convention) electric charge is carried by electrons and so a flow of electrons is also a flow of electric charge. But the negative sign of the charge means that the electric current (due to the flow of electrons) is in the opposite direction of the electron current.

If the charge on the electron had been deemed positive rather than negative, then the currents would be in the same direction.