Conventions about current flow
Direction of the current flow
A flow of positive electrical charges give the same electrical current as a flow of negative charges in the opposite direction.
Conventional current
Conventionally, in a circuit, the current leaves the most positive voltage of the source (battery) and goes back to the most negative voltage of the source, through the circuit it supplies.
The conventional current is positive in the direction of positive moving charges, and negative in the direction of negative moving charges.
In solid metals (wires), the positive charges carriers are immobile, only the negatively charged electrons flows.
Because the electrons carries negative charge, the electron motion in a metal is in the direction opposite to that of conventional (electrical) current.
Reference direction
In circuits, the direction of the current through a specific current is usually unknown.
Each circuit element is assigned a current with an arbitrary chosen reference direction. When you solve the circuit, the circuit element currents may have positive or negative values.
A negative value means that the actual direction of current through the circuit element is opposite that of the chosen reference direction you had assigned.
In electronics, it is assumed that all currents flows to ground or to 0v or to some common point (or back to the most negative voltage of the source). This usually matches conventional current direction, because power rail is positive in most cases. When using split supplies and negative rails, current will conventionally flow from the most positive voltage to the most negative voltage as indicated per an amp-meter.
