It wont' feel like it right now, but you WILL be ok and you WILL get through this. You must be nervous and anxious, but in time you'll recover, get to grips with your new 'friend' and start to feel healthier and better than you have in a long time. An ostomy really isn't that bad at all. You very quickly get used to it and find you can pretty much do and wear anything you want.
Start very easy on the food front and even if the Dr's and nurses tell you 'to eat what you like' don't! Start the first few days on liquids, jelly, soup etc.. then progress slowly to soft foods (mash potato etc) and from there gradually introduce low residue foods and see how you go. Keep your fluids up and include salt in your diet from the beginning (without a colon we don't absorb electrolytes in the same way).
Any issues with the bag etc, then post them here and we can help.
Good luck with the surgery and keep us posted! One step at a time. Deep breath. Welcome Sheila