Your app begins the certification process when you upload it to the Store. During the upload process, we check your app's packages for technical compliance with the Certification requirements for Windows apps. If your app passes these tests, you'll see a successful upload message under the upload control in the Packages page.
If a package fails an upload test, you'll see an error message. See Resolving package upload errors for possible errors and their resolutions. Correct the error and upload the package again.
After you upload the app's packages and you submit your app for certification, the packages are queued for the automated tests.
The first test checks your app's packages for viruses and malware. If your app fails this test, see Malware scanning in Resolving certification errors.
Technical compliance is tested by the Windows App Certification Kit. For info on how you can test your app with this kit before you submit it to the store, see How to test your app with the Windows App Certification Kit.
Content compliance is tested manually by a person. How long it takes the tester to complete this test depends on such factors as how complex your app is, how much visual content it has, and the tester's backlog of work.
Tip Describe any steps or procedures that can help make it easier to test your app in the Notes to testers page.
At the time you specify, either on a specific date or as soon as possible, we send your signed app to the servers and its description appears in the Windows Store catalog.
Note It might take some time for your app's listing to appear in search results. This is normal. Also, you can't change a release date after you submit the app to the Windows Store, but you can cancel the release, update the release date, and re-submit.
After your app passes the certification testing, its packages are digitally signed to protect them against tampering after they have been released.
Note You don't have to sign your app's packages before you submit them to the Store. We'll sign them for you after they pass certification testing.
Important When this phase begins, you cannot cancel your submission.
After the certification process completes, you get a certification report, whether your app passes certification and is listed in the Windows Store or not.
If your app fails one of the certification tests, you will see this on the report. Resolving certification errors has more info on how to fix your app so you can submit it for certification again.
This content is from MSDN http://msdn.microsoft.com/en-us/library/windows/apps/hh923026.aspx