Basic parts and functions of an analog multi tester?

It is a moving-coil galvanometer with a selectable array of shunts and series (bobbin) resistors. Shunts are also resistors but they go in parallel to the meter to restrict current through the meter itself and allow the meter to measure total current flow. The meter is connected in series in the circuit where you want to measure the current and the resistances are low. Series resistors are large and restrict current through the meter as well but the meter is connected in parallel to measure voltage drop. The maths and principles are very simple if you draw them out even if they don't seem so from a description. Resistance measurements are usually a simple current measurement and the meter is calibrated to follow Ohm's law. In old meters (such as the big black AVO meters from 50 years ago and more), for improved accuracy, a special extra "standard" cell was fitted solely for resistance measurements.