It's normal to get Braxton Hicks through out pregnancy. I get them usually around 16 weeks on. I have an irritable uterus - or have with the past pregnancies. I seem to be doing well this time with not nearly as many as I used to get!
A BH contraction is a tightening - your belly will feel hard. It can get really uncomfortable. I've had it be painful...not the contraction itself, but the way it squished the baby, it would sometimes hurt. If the contraction itself is hurting, then it's labor. But they don't consider it active labor unless your contractions are closer together. I never call until my contractions are about 3 minutes apart (or 5 minutes, if the hospital is far away). By then my contractions last about a minute each.
To time them, you start timing at the beginning of a contraction to the end. That gives you the length of a contraction. Then to time how often they are coming, you time from beginning of one contraction to the beginning of another. So, you're timing two things - how long each contraction is and how long from one to the next.
I get a ton of contractions for weeks at the end. It gets really annoying. I used to wonder when I would know when I was in labor, but when it starts, there is NO doubt in my mind!
I have had timeable, uncomfortable/slightly painful contractions that have lasted for hours and have come every five minutes, lasting about a minute, and my hubby was really worried. I knew I wasn't in labor, but he really wanted to go to the hospital, so we did. I wasn't in labor.
I have a different mindset than other ladies here (not that there is anything wrong with theirs!), but I tend to play it really calm and don't do anything about going in until there's no doubt I'm in labor. Each woman is different, though. I'm one who definitely feels a lot of pain in labor. There are some other women that don't feel pain while in labor until a while into it and then they have the baby in an hour or less. If you're ever concerned, go get it checked. But braxton hicks are SUPER normal and common. I wouldn't go unless they are timable, coming every five minutes, lasting for around a minute, and won't go away if you take a bath or something.
Good luck!