1.
Wicca is in no way evil. There are many types of Wicca, but none of them are evil in any way; the differences between them are very small.True Wiccans don't practice anything that has to do with evil; it is a nature and fertility religion (as well as Pagan of course, but there are some evil Pagan religions; Wicca is not one). We believe in Karma, so any harm done to another person will come back at us 3x. It is very peaceful, based on love and respect for the planet.
Although some people define evil as that which is not of their Deity. This is particularly true of the Abrahamic religions. Since Wicca is not of that deity, adherents to these religions term Wicca as evil. This only applies to those who have this definition of evil.
2.
Some Wiccans are:
+Monotheistic, recognizing a single supreme being, "The All" or "The One"
+ Duotheistic, worshiping a female Goddess and a male God, "the Lady and Lord"
+ Polytheistic, recognizing many ancient Gods and Goddesses, like Pan, Diana, Dionysius, Fergus, etc.
+ Atheistic, viewing the Goddesses and Gods as symbols, not living entities
3.
Since I'm not as familiar with Roman Catholic, I'll compare Wicca with Catholicism in general:
Catholicism is a "set" religion. There are no true variations.
Wicca has many variations, and can be combined with like religions; it's more of a personal thing. It has no set of rules, as long as you "harm none".
Catholicism is monotheistic. That is there is only one God.
Obviously Wicca is not monotheistic in nature. (see answer to question 2)
Catholicism teaches that there is a Devil.
The Wiccan religion does not believe in the Devil. For any of you who have heard that we are Devil worshipers, it's just plain not true! We don't think he exists. We see good and bad in everything. This being said, in some Wiccan beliefs, some of the gods have dark sides as well as good.
Catholics pray for guidance.
Wiccans use spells for help.
Catholics believe in one Baptism.
Wiccans don't get baptized unless maybe they have incorporated it into their religion or were baptized before becoming Wiccan.
There are other Sacraments, six in total.
Wiccans don't have this; we have what is called the "Wiccan rede", which is the closest to a set of rules that we have.
Catholics have a Bible.
Wiccans have what we call a Book Of Shadows. Traditionally, in a Wiccan family, this book is passed on from generation to generation. It contains spells, herbal remedies, cooking recipes, favorite bits of poetry- whatever they decide to put in it. Some may only have spells.
4.
Wiccan holidays:
October 31 -- November Eve -- Samhain
December 21 -- Winter Solstice -- Yule
January 31 -- February Eve -- Imbolc (Oimelc) or Brigid
March 21 -- Vernal Equinox -- Ostara
April 30 -- May Eve -- Beltaine
June 21 -- Summer Solstice -- Litha or Midsummer
July 31 -- August Eve -- Lughnasadh or Lammas
September 21 -- Autumnal Equinox -- Mabon or Harvest Home
Wiccan Sabbats (festivals):
Samhain- near Halloween
Yule- December 21
Brigid- February 2
Ostara- around March 21
Beltane- May 1
Litha - about June 21
Lugnasadh (Lammas)- August 1
Mabon- near or on September 21
And I'll tell you a little bit about one of each.
Holiday
June 21 -- Summer Solstice -- Litha or Midsummer
On this day, the noon of the year and the longest day, light and life are abundant. We focus outward, experiencing the joys of plenty, tasting the first fruits of the season. In some traditions the sacred marriage of the Goddess and God is celebrated (in others, this is attributed to the springtime holidays). Rhea, the Mountain Mother of Crete, has breathed out all creation.
Sabbat (festival)
Beltane
or May-Day, is a celebration of love.
It is one of the most important festivals the year. The word Beltane literally means, "shining fire." This is one of the most exciting festivals of the Wheel of the year. It is also one of the only holidays that is usually celebrated in the light of day. The collecting of spring flowers is one of the popular customs of this day. For thousands of years, people would go into the fields to collect the pretty flowers and exchange them.
Towns people would often proceed through the village streets putting flowers on all the houses and buildings. People inside the homes would offer them wonderful food and goodies to eat as sort of a spring version of "trick or treat." Another benchmark tradition of this holiday is the Maypole. In tradition, a fir was used. The young, unwed men would go to the forest and return with the tree that would be fashioned into the pole. The pole was brought to the center of the village to be guarded through the night until the first day of May. On that day, the people would come and dance around the maypole clockwise to bring fertility and good luck. Later, brightly colored ribbons were woven around the pole by the dancers as they wove around eachother. This symbolizes the balance of masculine and feminine energies and the duality of life. The ribbons would then be removed and kept in a safe place to be burned in the Beltane fires of next year. This action represents the old dying to give birth to the new.
Fertility is a central theme of Beltane. The people lived in close connection with the Earth. To have food to eat, the crops and the beasts of the fields would have to be fertile.
In the time of the ancients, this was a life and death matter. For this reason, we have a number of holidays and rituals that are connected with fertility. The maypole is connected to this theme by way of the view point of it being a phallic symbol.
Another fertility representation is the custom of jumping the cauldron. Couples wishing to conceive children will jump the cauldron together. Fertility of all areas of life are invoked during this holiday as well as sexual fertility. This is the day for Wiccans to laugh and banter about having the most joyous of times!
Can you be Wiccan and still worship God?
Yes, and you can even combine some Christian religions with it... but not Catholic, as it is completely against other religions.
When a Wiccan worships god, they do their magick (like spells) through God, and ask him to guide them and do his will. And of course, like the Wiccan rede says, you only use it for good.
I don't know why anyone would say otherwise; because the Divine is the same for everyone, just a different name. So for example: when people believe in more than one God, combined they are actually just one God. One God is a big concept to understand so many cultures divide him into many or a few gods/goddesses.