Dates of Filing vs Final Action .. can someone explan this to me in laymans terms and where does priority date comes into play and is it even relevent any more ?

this is for eb3 btw.

Date of Filing - the date when you prepare and file your permanent residency application.
For e.g. in your case, which is EB3, oh wait a minute...yours is already Current, why are you worried?
Final Action Date: is the date when the concerned authority USCIS/DOJ will give The Final verdict on your Application, whether it is approved or not.