For Software Developers/Providers

Personal Package Archive (PPA) service is provided for Ubuntu by Launchpad via which you can distribute software and updates directly to Ubuntu users. Create your source package, upload it and Launchpad will build binaries and then host them in your own apt repository.
Refer this link for more on how to create your own PPA to distribute software.

For Users (Like Us)

PPA (https://launchpad.net/ubuntu/+ppas) can be easily used to add new sources for software not available in Software Centre.PPAs work like normal Ubuntu archives. You can install software in the usual way — for example, through apt-get or synaptic — and whenever there’s an update Ubuntu will prompt you to install it. Both the x86 & x64 architectures are supported by PPA.

Here is an example, to add the repository:

sudo add-apt-repository ppa: user/ppa-name

So pop up your Terminal and try adding few of them from below

Open Office : sudo add-apt-repository  ppa:openoffice-pkgs/ppa

Google Chrome Browser Beta : sudo add-apt-repository ppa:chromium-daily/beta

ClamAv Antivirus : sudo add-apt-repository ppa:ubuntu-clamav/ppa

Remember to run sudo apt-get update after you are done with above

Here is a look at a successfull addition via PPA

If you still feel you are bit of a Linoob just try using Ubuntu Tweak