There are a couple of ways of freezing spinach. I don't usually get around to freezing it because we usually eat or give most of it away.
My sister Lisa told me that she takes her fresh, washed spinach and just throws it in a freezer bag. Then when it freezes she opens the bag, crumbles it while it's in the bag and then removes the air and freezes. She sneaks it in to things like spaghetti sauce, casseroles, and soups. I also do this. My daughter and husband both like spinach so I guess it's not necessarily sneaking it in, but it always adds extra nutrition to things.
I read online somewhere that freezing without blanching isn't the most nutritious way. I read that all veggies have enzymes and bacteria that break down the nutrition and taste over time if they aren't blanched. I need to look into that a little more. To blanch greens you should get a pot of water boiling. Throw the spinach in the pot and let boil for 2 minutes. Immediately take it out and put in an ice water bath. This is to stop the cooling. Then you could bag the greens, but I might suggest freezing on a cookie sheet lines with wax paper before you put it in the baggie. That way it won't end up as a big lump of spinach. You could also try to crumble it after you put it in the bag.