You have to be approved to upload to the official repositories. This allows a level of trust to be established between the maintainers and users of the packages on the system.
On top of that, it is unlikely you actually want to do this, because it would require a whole set of requirements and you'd have to learn to properly maintain your software and packages.
Instead, you can create your own repository, and those who trust you (ie: you yourself) can add the repository to their system and pull in your packages. These are referred to as Personal Package Archives, or PPAs, and Launchpad offers such a service.
Even if your end goal is to have your software in the official repositories, this will get you started learning how to package and maintain properly until your software is shown to be wanted in the official ecosystem. Or, you can use the PPA forever and not worry about anything else.