How to decipher capacitor markings
Take a clue from the black silkscreen painted on the printed circuit board surface:


C as in C20 is some kind of capacitor. Most of those you've circled are not polarized and could be mounted either way.
R denotes a resistor - can be mounted either way.
T denotes a transistor, additional silkscreen show "E"(emitter), "B"(base), "C"(collector)
D denotes a diode. A silkscreen diode symbol shows which direction the cathode points.


The numbers following each letter allow multiple resistors to be uniquely identified...a schematic diagram would also show this letter followed by a number, and most often its value.

An example might be C4 220n...This is a capacitor, value 220 nanofarads. The silkscreen doesn't show the value, whereas the schematic diagram should.