A circuit can consist of thousands of components, but the most important ones are the voltage or current source, the consumers and the wires connecting them. In the case of PCBs, the "wires" are called traces. Where a wire connects to another wire, it is a node (or junction), direct paths between nodes are branches, and when starting from a point the same point can be reached through multiple branches, it is a loop.
The diagram below shows a circuit with a voltage source and two parallel resistors. It is important that the branches are horizontal and vertical lines and the nodes are marked by clearly visible dots. There are many ways to draw the voltage sources, including a separate way for the cells of a battery.
Node
Branch
Loop
Ammeter
Voltmeter
Fuse
Charges move from the negative pole to the positive pole. The direction of the current, on the other hand, is reversed, from the positive to the negative pole. Calculations and circuit design both follow this rule.