Need VST and VSTi help in cubase (MAC)

I have few questions about new Cubase 8 LE and VST and VSTi Plugins on MAC (Yosemite)
1- Whats the difference between VST, VST2 and VST3 ?
2- Which of those vst plugins can i use in Cubase 8 LE ?
3- Can i use my old VSTI and VST plugins from CUBASE 5 ?
4- Where does VSTI and VST plugins goes on a mac computer ?

Thank u and sorry for my bad english :frowning: