Usually low voltages or DC(Direct Current) is used by the electronic circuits, because load does not need very high power and just a few capacitors, resistors, I.C or other components will not require much power to perform their jobs and it will be powered by a 18650 lithium battery or any other battery source with required voltage and current.
Schematics use symbols to represent components in the circuit. Conventions are used in a schematic to represent the way electricity flows. The common convention we use is from the positive to the negative terminal. The realistic way electricity flows is from the negative to the positive terminal.
Electric circuits are different than electronic circuits.
A schematic is a diagram of an electrical circuit. Schematics are graphical representations of the essential connections in a circuit, but they are not life-like depictions of a circuit.