Use it exactly like you would use normal green spinach. Both the leaves and stems are edible.

Here is a link to some great recipes and will give you abetter idea of what to use it for.
http://www.organicauthority.com/meatless-monday-chard-recipes

As far as freezing goes: I
1)Wash the leaves,
2)Remove the stems by pulling them out : Hold the stem in your left hand while sliding your right hand up the base of the leaf, stripping off the green bits. Much faster than cutting it with a knife.
3)Make sure it's nice and dry and then freeze.
If you blanch it before freezing it goes yucky when cooked, while cooking it raw from frozen holds the texture better in my opinion. Its also a great way to stockpile if you only have a couple of plants and can only gather a few leaves at a time.