iTunes Connect is a suite of web-based tools that allows you to submit and manage your applications for distribution on the App Store. In iTunes Connect, you will be able to check the status of your contracts; set up your tax and banking information; obtain sales and finance reports; request promotional codes; and manage users, applications, metadata, and your In-App Purchase catalog.
If you plan on selling your app, you need to have a paid commercial agreement in place so that it can be posted to the App Store. You will have to request a contract pertaining to iOS Paid Applications. All this is done through iTunes Connect under the Contracts, Tax, and Banking links.
When requesting contracts, beware of potential issues that can occur, such as delays when Apple processes your information for the first time and/or issues when changing your current contact information in iTunes Connect (that is, change of address if you have moved to a different location). It is your responsibility to regularly contact Apple for support to make sure that the information is always up to date in your contracts.