I know everyone says this and its annoying but you will know when you're having a real contraction lol it'll stop you in your tracks, the pain can radiate from your back to your abdomen or just be in your abdomen and your tummy will tighten up.

with both of my pregnancies my contractions felt like really bad menstrual cramps that got worse as labor progressed and your belly will tighten when you have one. if your belt is tightening with not very much pain is most likley Braxton hicks contractions. I know with my second son I was having contractions for 2 weeks before I had him.