Anyone experienced implantation bleeding

I was wondering what your experience was with an implication bleed I see lots of references to it but no clear idea of what it is like with a BFP.

Could anyone who has had an implantation bleed and is pregnant describe to me what it was like please? 

Is it different from spotting before a period AF? Can you tell if it is an implantation bleed? Is there a difference between AF bleed and implantation bleed?