N.B. There is no chain included. You will need to source and fit your own 1mm thick chain. Silver chains are readily available on ebay.
It can be tricky to attach the pendant to the chain because the chain needs to go through the very small eye in the top of the pendant. This will probably mean removing the clasp from the end of the chain and soldering (or glueing) it back on again after you have threaded it through the eye. I have had success using chain from ebay, snipping the clasp off, then glueing the clasp back on with a tiny dab of Araldite.
Alternatively you can use a jump ring to join the pendant to the chain and then closing the jump ring with a pair of pliars. Again jump rings are readily available on email