Beginner Led Soldering Connection Project
Take a look at this calculator:

http://ledcalc.com/

You can find V forward (voltage drop) for your LED color in tables such as these:



If your LED looks like the following image then the typical current would be 10~20mA.





You'd want to find your LEDs current vs Vf graph such as the one above, then plot and find the Vf for the current you want it to operate on, then use the formula:

Vsupply - Vf*(number of LEDs) = current * resistance

Then round "resistance" to the closest standard value. (I'd round up for lower current).