Galvanometer A very sensitive meter used to measure tiny currents, usually 1mA or less.
Transistor NPN A transistor amplifies current and can be used with other components to make an amplifier or switching circuit. This symbol is for a bipolar junction transistor (BJT), the type you are most likely to use at first.
Amplifier (general symbol) An amplifier circuit with one input. Really this is a block diagram symbol because it represents a circuit rather than just one component.
Logic gates process signals which represent true (1, high, +Vs, on) or false (0, low, 0V, off). For more information please see the page on logic gates. There are two sets of symbols: traditional and IEC (International Electrotechnical Commission).