Press "P" to bring up the preference tab, under file go to VST settings. There you can add and remove folders
but most importantly for you right now you can scan your vst folders.
The plug manager wont be of any use until your VST's have been scanned.
Once done you might need to make sure that your plug in layout is set to, "Default all" You'll set it when you add an effect by right clicking in an fx box, at the top it will say plug in layouts.
Hope that helps
Steve