This one is on just preparing it. If you want pumpkin recipes, see The Great Pumpkin e-book, available for free.
The simple version is: cook until soft, mash or puree, use or store it. If you need details, this is the post for you!
I prefer to steam my pumpkin, that way I can keep the skin on and get the extra fiber and minerals from it, and waste less. You can bake it if you prefer; cut in half, clean out the insides, and bake, cut-side down on a cookie sheet. Plan on about an hour at 350 degrees. Baking is a better option if you're using a thick-skinned squash like Hubbard or Acorn (which work fine in pumpkin recipes, by the way).
If you're steaming it, start by scrubbing off any dirt. If there are little blemishes, cut them out or scrape them off with a paring knife. Some are only skin-deep. Cut off the steam and blossom end. Those little brownish-grey bits never will soften up. They won't hurt you, but they're not pleasant to eat.
Mash with a potato masher if that's all you have (but it won't get rid of strings). I use a blender and usually have to add about 1/4 c. of the cooking water to get it to puree. A food processor would work great.
So that the bags lie flat for storing, you can freeze them on a cookie sheet. This has another benefit- if your bag happens to pop open while freezing, spills are caught on the tray. Yep, I learned this one the hard way. Actually, they'll stack in a less space if you freeze them already stacked up. Just make sure those bags are going to stay closed!
This reminds me of a quote seen today: "Always learn from others' mistakes. You can't possibly live long enough to make them all yourself."
To bake them instead, drizzle with 1-2 tablespoons of oil (this makes them MUCH easier to chew and digest!), sprinkle with salt, and bake until they've turned golden brown. Use any temperature from 350 to 400 degrees, baking will take anywhere from 7-20 minutes, depending how wet they were and how hot the oven is.