Can someone educate me on implantation bleeding?

I'm not looking to get pregnant anytime soon but I am curious. my boyfriend and I had a little pregnancy scare a while back when my period was about 4 days late and once I started again, we became quite overjoyed. I mean we want kids but not for awhile. but anyway, the reason I'm curious is I had a friend of a friend of mine, who is a mother to 3 kids with the youngest being 6 months, tells me to check my bleeding that what im experiencing could be implantation bleeding instead of period bleeding. she told me that if I were wearing tampons (I wear pads and tampons on my period for double protection and since this one in particular was late, it resembled more opening of floodgates, as if my body was holding back all the blood it could for 4 days and then it all came at once in my bare underwear) and if I was pregnant that it would hurt the baby. she also told me to check my pads for clots and if I didn't see any then I could definitely be pregnant. I even tried Googling it to study the subject further, but I basically learned nothing. which is why i ask, can anyone care to educate me on the matter?