1. Go to http://www.frostwire.com/downloads and select the option to install FrostWire on Mac OSX
2. Depending on your browser settings, the installer will either directly to the Downloads folder, to another folder your've specified or will ask you where to save it.
Go to that folder and double click the installer - file name is frostwire.dmg
Sometimes your OS might ask you if you are sure you want to open an installer you downloaded from the internet. Click 'Open'
3. First Installer Wizard screen will appear - double click the FrostWire logo.
4. Accept the terms and conditions and navigate through the Setup Installer Wizard. FrostWire may also suggest you to install additional software that helps to support the future development of the app (you can always "Decline" these offers is you desire to).
4. Wait till the installation status completes to 100%
You might have to enter your system password. FrostWire does not need any special system permission - the password is required because the software will be directly installed into the Applications folder without specifically giving you the option to choose the folder.
5. Few more seconds and the installation should be complete. FrostWire will open automatically and let you set up your preferences before downloading. Click Finish on the Installer to close it.