Re: LEDS
Bear in mind the following. No two diodes have exactly the same characteristics. Since current flow and light output are exponentials of the applied voltage, any mismatch is easily discovered. When wiring diodes in parallel, unless they are matched, or near matched, one diode will bias (light up) at a lower voltage than the other. (One may glow brighter than the other). If you are using the same type then wiring in parallel off of a single source might work. But in any case limit the total input current with a resistor or limit the branch currents with individual resistors.
If you are using different colors, the diode band gap voltages (a function of the semicondutor material) will be different. What this means is that one diode may be completely on at a given voltage while another is not. Current limiting resistors will solve that problem.
The long lead is referred to as the anode, the short is the cathode. Apply the higher potential to the anode.