I'm new to electronics. I know what resistors do, what don't understand why they're needed, or how you know if they are. I was running all lights on this thing without resistors and it worked fine? I ran it for at least 45min.
The reason you need current limiting resistors is that LEDs have an approximately constant voltage drop across them, of about 1.5-3.5 V (depends on the colour and type), if you apply 5 V directly from your Arduino, then you are forcing the remaining voltage to be dropped by the diode, and so it draws a very high current, if you keep doing this with too high voltages for too long, you will blow your LEDs. If you put a resistor in series with the LED then the remaining voltage is dropped across the resistor, and this voltage drop (about 3.5V) divided by the resistance you use will tell you your current through the LED. It varies between LEDs but it is usually advised to keep this below 15 mA