Step 1: Parts & Assembling:
1. One LED
2. One resistor - one kilo-ohm resistor
3. One mobile battery
Connect the 1K resistor to the positive of the LED. (Or to negative; resistor to any side)
Connect this positive of LED to (outside) positive of the mobile battery.
Just bend and manually connect the LED leg to the mobile slots.
NEVER solder directly to a battery.