Early Labor: This phase of the first stage is where you will spend the most time. This is characterized by contractions that are regular but not be very close together or last very long. The contractions maybe 10 minutes apart and last only 30-45 seconds. This is a very comfortable stage of labor for most women and a chance to ease into labor.
Active Labor: As the contractions become more intense you will move into active labor. Here the contractions are regular and are coming closer together and lasting longer. They may be 3-5 minutes apart and last up to 60 seconds. This is the serious phase, where mom gets down to work and really uses many of her coping techniques.
Transition: The hardest, but shortest phase of the first stage of labor. Transition is what television births are all about. These contractions are stronger and longer and finish dilating the cervix. The usually last 90-120 seconds with breaks of about as long in between. Generally this phase only last for 30 minutes to 2 hours.
Many people will try to tell you how many centimeters you should be dilated in each phase. I'm generally not a big believer in that way of defining the stages of labor. You can be exhibiting transition like contractions and only be 4-5 centimeters, but still really close to having the baby. It's important to remember that very few women will be dilated 1 centimeter, 2 centimeters, 3 centimeters, etc. Many women will jump in dilation. And some will even have stories of being 4 centimeters dilated and then be completely dilated within a few minutes. So it's more important to pay attention to the intensity of the contractions and how they are coming than what the cervix is doing for most women.