Hi Voyager,
LEDS are a doddle.... just got to remember to connect them the right way around....for single colour LEDs, ignore all the advice about long leads and short leads and flats on the passage. Look at the electrodes in the package, one will be cup shaped the other will be smaller. The cup shaped one is the cathode - this connects to the negative. The other end connects to the positive.
Use a resistor - it can go on either side of the LED. It can also go at the far end of the connecting lead. If you don't use a resistor, the LED will glow very brightly for a fraction of a second and then explode. For a 6V system use 220Ohm (Red-Red-Brown or Red-Red-Black-Black) for red LEDs and use 100Ohm (Brown-Black-Brown or Brown-Black-BLack-Black) for Green and Yellow. For White LEDs iit depends if you want a glow or a light. Remember, though, that while LEDs have a blue tinge to them. Try to use one resistor per LED rather than sharing. Use commonplace 0.25Watt or 0.5Watt metal film resistors.
The other thing is the type of LED - high-brightness types have a much narrower field of view, normal LEDs a wider one.
Wom