| This is for beginners and very much by a beginner.
It's intended to get an intuitive overview for hobbyist needs. It may get you started, but to be able to do anything remotely clever, follow a proper course or read a good book.
Some basics and reference: Volts, amps, energy, power · Ground · batteries · resistors · changing voltage · transistors · fuses · diodes · varistors · capacitors · inductors · transformers · baluns · amplifier notes · frequency generation · skin effect
And some more applied stuff:
Sensors: General sensor notes, voltage and current sensing · Knobs and dials · Pressure sensing · Temperature sensing · humidity sensing · Light sensing · Movement sensing · Capacitive sensing · Touch screen notes
Less sorted: device voltage and impedance, audio and otherwise · Common terms, useful basics, soldering · Arduino and AVR notes · ESP series notes · PLL · signal reflection · pulse modulation · electricity and humans · resource metering · Microcontroller and computer platforms · SDR · Project boxes · Unsorted stuff
See also Category:Electronics.