There are many different Pagan paths out there, and many are capable of some degree of personalization.
Pagan religions - according to most of the world - are anything that isn't Christianity, Judaism or Muslim. But if you are part of the Pagan community, the general consensus is that it is any nature-based religion, including reconstructions of the pre-christian religions of our ancestors.
Most - if not all - Pagan paths have a high respect for nature and the cycles of the seasons. Many are polytheistic (believe in more than one God) though monotheistic or even atheistic are common. Some people believe that all Gods are One God, but there really is no set rule.
Common Pagan Religions (Not Including Magical Practices)
Wicca - Modern Pagan religion founded by Gerald Gardner in the 1950s. This is usually the first Pagan religion people hear about. There is a belief in both a God and a Goddess - the Lord and the Lady - and the main rule is "Do as you will, but harm none."
Heathenism - A Norse Pagan reconstruction. Many followers try to practice as closely as possible to the way their ancestors did. There is strong roots in family, and most Heathens are Germanic or Scandinavian of some sort. They worship the Norse Pantheon, and believe in the Nine Noble Virtues.
Druidism - A Celtic reconstruction religion. (Need more information.) Druidism is very nature-based and promotes peace and balance.
A good place to start when looking for your specific path is to read the basics of Wicca, as it isn't a reconstruction, but a newer religion all together. From there, read up on the mythology from different pantheons, and if you feel a strong pull to any of the Gods or Goddesses check out the religion of the people who originally worshiped them.