iTunes Connect is used to submit and manage your app. After you've created an Apple Developer account, you can use the same credentials to log in to iTunes Connect.
Once you've logged into iTunes Connect, you should see a screen that looks similar to the one below.
If at any time you have any questions about iTunes Connect, please refer to Apple's iTunes Connect Guide.
In the meantime, continue to the next step in the distribution process: How to Fill in an iTunes Connect App Listing.