Hello,
I admit that I am not McGyver... and I can't make fire with only a drink can and a bar of chocolate.
Fortunately many people know how to do it and it's easy to find a lot of videos on youtube: I have to polish the base of the can with the bar of chocolate, the idea is to get a surface like a mirror and use this part and the sun to get the fire. The important things: cans and chocolate.
Encarna