Transistor PNP 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.
Thermistor A transducer which converts temperature (heat) to resistance (an electrical property).
Light Emitting Diode A transducer which converts electrical energy to light. Usually abbreviated to LED.
A rheostat has 2 contacts and is usually used to control current. Uses include controlling lamp brightness or motor speed and changing the rate of flow of charge into a capacitor in a timing circuit.