I think that trying to describe what is a contraction feels like is impossible. I have had three births and each time the contractions felt different!!!! My first was a back to back labour, and all the pain was in my back, none in my stomach,also I was caught by surprise that I got some contractions coming one on top of the other with no break in between, this scared me. Second time, there was a sensation of intense cramping starting in the low tummy and gradually creeping upwards til the pain was in my whole tummy and back. It came in the classic "wave pattern". With my third, I thought I had a little trapped nerve one side of my lower pelvis, it was only when it happened the third time that I wondered if it was contractions!!! I continued chatting online here online on MN while using a contraction timer online, to discover three contrations later that they were 4 mins apart lasting a minute and I suddenly went "oh I am in labour!". So despite it being my third labour I did not know for half an hour that it was for real labour!!!!!
But I also had plenty of false labours with each of them, with contractions coming regularly at as little as 3 minutes apart and the midwives saying you will have your baby tonight, only for it to gradually go away again!!!!!
So for me the contractions never meant that labour was imminent, but when it was real labour and I was about to give birth, I knew it was happening and I could think of nothing but what my body was doing.
I think that the main thing is not to panic, easier said than done, know that the pain will go away and "breathe, breathe, BREATHE!"