RFC Vs Class/Interface

Hi,

I have created a Class using SE80 using Class/Interface option. Can anybody please explain me what will be difference between

RFC and Class Interface. Whether Class Interface can be used as same RFC?

If yes how class can be accessed from other legacy systems?

Whether we need to right a wrapper RFC for this class to access?.

I heard BAPI's also global classes that have BOR entries.How these BAPI are accessing from legacy?

I am very new to ABAP

Thanks

SAR