To launch POL, simply use a terminal and type playonlinux but, most package manager generate a shortcut for POL, in "game" section.
If you want to install a supported game/app, simply use POL, use search engine in "Install" menu of POl and follow instructions, it's quite simple.
If you want to install unsupported game/app, first thing to do is check AppDB, is your game/app is bronze or garbage rated, forget it.
If you want to create a POl installer for your game/app, check other scripts on website an examples, you can "play" with POL commands using "POL terminal" in options. Be sure to respect POLv3 current standards, a game like Dead Space respect thoses standards, it's a good example.