If you want to download and install the Adobe Flash Player from the Adobe website you will get the following message:
NOTE: Adobe Flash Player 11.2 will be the last version to target Linux as a supported platform. Adobe will continue to provide security backports to Flash Player 11.2 for Linux.
If you want to install the Flash Player plugin on Ubuntu 13.04 all you have to do is to open a terminal window (press Ctrl+Alt+T) and copy+paste the following line:
sudo apt-get install flashplugin-installer
When the Flash Player is installed close the terminal window and restart your browser.