Conventionally, electric current is supposed to flow from higher potential to the lower potential point. The positive electric charges are supposed to flow from positive terminal of the battery (at a higher potential) towards the negative terminal (at lower potential).
Since positive charges (ions) do not move in a circuit and only electrons (with negative charge) move from the negative terminal towards the positive terminal. This creates current equivalent to the movement of positive charges in the opposite direction.
2) In a battery there is a lot of chemical energy stored in terms of the ions in the electrolytic solution. When the circuit is closed between its terminals, there is a path created for the charges to flow from one electrode to another electrode. The driving force is the potential difference between the terminals. Due to that potential difference, there is an electric field created. Due to the field, an electric force acts on the charges, and the charges get accelerated along the circuit.
3) SI unit of current : Ampere ,
Volt = Ampere Ohm
Coulomb / second = Ampere
4) we can connect a device called an ammeter to measure current flowing in the circuit. It is connected in series with the conductor in which we want to measure the current.
we can measure current in milli Amperes, micro amperes..