What's the difference between Braxton and true contractions?

Jen • Pregnant with #2 ❤️ Due June 13
What's the difference between Braxton hicks and true contractions? Today my stomach felt extremely tight like a ball and then would release a minute later and lead to very mild
period-like cramps. This is my first pregnancy and I'm scared I won't know when to be concerned and go to hospital unless my water breaks which will be obvious. Are true contractions painful and the tightening sensation just Braxton hicks? 36 w 1 d