The difference between Paganism/Wicca is Paganism is an umbrella term. Paganism is used to describe any religions outside of Christianity, Judaism, or Judeo-Christian. Wicca is a form of Paganism, meaning it is a religion that falls under it.
Paganism describes a number of religions, such as: Wicca, Taoism, Satanism, Buddhism, Sikhism, etc. Wicca is just one particular religion that falls under this umbrella term. Wicca is derived from the word, "witchcraft". Because the word "witchcraft", has so much negativity attached to it, because of Christianity and the Bible, the name "Wicca", was created to describe the religion of witchcraft.
There is a common misconception that all Pagans are witches, and that all Pagans are Wiccans. This is not true. As stated above, Wicca is just a religion, that falls under the term of Paganism. It is not the same. Not all Pagans are witches, and not all Pagans are Wiccans. There are some similarities in both Paganism and Wicca. For example, the symbol of Paganism and Wicca in particular, is the pentacle. The pentacle is a symbol for the five element: fire, water, earth, air and spirit.
In Satanism, the inverted pentacle is utilized. Satanism, though many Wiccans will disagree with this, is a form of Paganism. Wiccans do not believe in Satan, Lucifer, or the devil as he is often called in Christian religions. They believe that he is simply a Christian entity. However, Satanism is Paganism, and Luciferian is a form of Satanism, so therefore Satan, Lucifer, and the devil, is found in Paganism, though he is not found in Wicca.
Paganism actually came years before Christianity. Wicca did not. Wicca is a more modern form of Paganism.
The term "Pagan" actually means "country dweller". The term "Wicca" means "witchcraft."
A person who considers themselves a Pagan, usually is polytheistic. Polytheistic means one believes in more than one deity, whether that is a god or a goddess. In Wicca, some believe in a just a God, some believe in just a Goddess, and some believe in both. There are even some who believe in a number of gods and/or goddesses. So, Paganism and Wicca is one in the same, yet different.
So let us review: To consider oneself a Pagan, you do not have to be a Wiccan. That is the major difference between Paganism/Wicca. If you are any religion outside of Christianity, Judaism, or Judeo-Christian, you are a Pagan. If you follow the religion of Wicca, then you are a Wiccan. That is the major difference.
Paganism does not have a founder. Wicca does. The founder of Wicca is Gerald Gardner. There are many Sabbats and Esbats that are celebrated in Wicca. Most people believe that these holidays are only celebrated in Wicca. This is inaccurate. These holidays, Sabbats, and Esbats are Pagan holidays. The Christians stole these holidays from the Pagans, in order to convert Pagans to Christianity.
In Paganism, you do not have to practice witchcraft. In Wicca, witchcraft is usually practiced, because Wicca is the religion of witchcraft. That is another major difference between Paganism/Wicca.