Your question is confusing since you ask first about Mountain Lion and then about Snow Leopard. If you really are looking for Snow Leopard, that has never been available for download. If you call the online Apple Store, they may still have copies of Snow Leopard available though it's no longer listed on the web site. If they no longer have it available, as has been reported in a couple of recent threads, you'll need to look to private sellers, and the prices are rising quickly. If you buy from a private seller, make sure you get the retail disk set (white label with a picture of a Snow Leopard), not the system disks from another model of Mac (grey label).
Forum Tip: Since you're new here, you've probably not discovered the Search feature available on every Communities page, but next time, it might save you time (and everyone else from having to answer the same question multiple times) if you search a couple of ways for a topic, both in the relevant forums and in the Apple Knowledge Base, before you post a question.
I have been looking in the Mac store and it will not let me download.
Don't know what "Mac store" is but if you have the Mac App Store, you already have Snow Leopard. Just go to the Apple menu in the upper left and click Software Update, which should bring you up to 10.6.8 which is needed for iTunes 10.7 with iPhone 5 support.
Start by checking if you can run it:
Requirements for OS X 10.6 'Snow Leopard'
Whilst Apple have withdrawn Snow Leopard from their stores, you can still get it from Apple by calling 1-800-MY-APPLE (if you are in the USA) and they will supply the SL DVD for $20 for a single user, or $30 for a family pack that covers up to 5 Macs. You can also purchase the code to use to download Lion from the same number (Lion requires an Intel-based Mac with a Core 2 Duo, i3, i5, i7 or Xeon processor and 2GB of RAM, running the latest version of Snow Leopard), or you can purchase Mountain Lion from the App Store - if you can run that:
If you are outside the US call your national Apple Helpline:
If you're in the UK, use this number: 0871 508 4400
When you have installed it, run Software Update to download and install the latest updates for Snow Leopard.