Elektronik?

Actually, the thing is simple: someone has to determine in which direction the current is counted positively, in which direction negative… This fixation is related to the voltage… because there is no natural negative resistance and U=R*I applies. Voltages can also be negative.

If nothing else is specified, you can specify the positive current direction. To do this, you will draw an arrow in the schematic. Or you give two connections of a component (e.g. resistance) names like A and B…

The positive voltage or the positively counted current flow is then the indication of the points:

Here the positive current would run from A to B:

Here the positive current would run from B to A:

In reality, a few conventions have formed… in a series connection, one would consider the same current direction as positive for each resistance/consumer… In the case of diodes, it is customary to apply the positive current direction from anode to cathode…