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.
To start installing software from a PPA, you need to tell Ubuntu where to find it and how to verify the integrity of the packages.
Adding a PPA to your Ubuntu repositories
Adding a PPA to Ubuntu takes no more than a couple of minutes.
Step 1: Copy the first line from the apt sources.list entries section of the PPA overview page. For example:
deb http://ppa.launchpad.net/awn-testing/ubuntu jaunty main
Step 2: On your Ubuntu computer, open System > Administration > Software Sources.
Step 3: Click the Third Party Software tab. (As of Karmic, this tab is named Other Software.)
Step 4: Click the Add button.
Step 5: Paste the line you copied in step 1 and click the Add Source button.
Step 6: Now copy the second line from the apt sources.list entries section of the PPA overview page and paste it in just as you did in steps 4 and 5.
When prompted, reload the software sources information. Don't worry if you see a warning about unverified software sources; we're going to fix that next.
Adding the PPA's key to Ubuntu
Now Ubuntu knows about the PPA. It also needs to know how to check the software hasn't changed since Launchpad built it.
Note: This is not an endorsement of any of the software in PPAs. You must make sure you trust the PPA owner before installing their software.
Step 1: On the PPA's overview page you'll see the PPA's OpenPGP key id. It'll look something like this: 1024/12345678. Copy it, or make a note of, the portion after the slash, e.g: 12345678.
Step 2: Open your terminal and enter:
sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 12345678
Replace 12345678 with the key id you copied in step 1.
Step 3: Finally, tell Ubuntu to re-load the details of each software archive it knows about:
sudo apt-get update
You're now ready to install software from the PPA, using a tool such as apt-get in the Terminal or Synaptic.
To publish software in your own PPA, you need to build a source package.