in the U.S.:
if you add a sub panel to, say, a garage on your property, remember also to add a ground wire from the sub panel itself, you'll most likely have to add a ground lug in the panel, and drive a ground rod into the ground outside the structure.
use solid copper wire, not stranded.
when you add breakers to the box, DO NOT use the common bus to attach the ground wire to.
as I said, you'll probably have to add a ground lug to the box as they normally do not come pre installed.
unless you obtain 4 conductor cable, when you "power" your sub panel, you'll have 2 hot wires, and a common.
this is so you can have 220v circuits coming out of the sub panel.
remember, get your ground as I outlined above.
if you use only 1 hot and a common, only 1 half of your sub panel will be live.
before you ask, yes, it will work without a ground.
but it is not safe.
I can offer more detail should anyone wish to know more.
remember, anytime you mess with any kind of electricity, if you let the magic smoke out, it won't work anymore.