UPDATE: For a crucial safety update and time saver head to Step 6
Step 1: The shopping list
>>1 USB wire, doesn't matter what kind as long as at least one end is standard USB A (look below)
>>1 3-5v LED
>>A sweets tin, in this case a small box from some garbage shaped sweets.
>> OPTIONAL: If your box or case has any plastic that is dark in colopur it will absorb the light more, if you cover this plastic on the inside of your box or case ((in this case at the top of the box there is a bit of dark plastic on the lid)) with a layer of tin foil, shiny side facing the light source, then your box will be better lit.
Also to ease the job along you should consider:
>>A standard pair of wire clippers
>>A handheld drill