3 resources.
Kirchhoff's Current Law and Voltage Law explained, with a fully worked two-loop circuit solved for all three branch currents.
How to reduce any linear two-terminal network to a single source and resistor, with a worked example finding the Thevenin and Norton equivalents of the same circuit.
The ideal op-amp assumptions, the inverting and non-inverting amplifier gain formulas, and worked examples computing the output voltage for each configuration.