Witches in popular culture come in many kinds and groups. This post will deal with identifying several of these types and give a sampling of each.
The Old Witch In The Wood. This is a very old and common type of witch. A solitary crone who dwells deep in the forest, she is often cannibalistic and sometimes rich. The witch in "Hansel and Gretel" is the most familiar example of this type; Baba Yaga in Russia is another, and the witch in "Old Gally Mander" from the United States another. She is a supernatural force, and she seems to embody hunger, either for flesh or riches.
The Three Witches. An extremely old grouping of witches, that may go back to the triple goddess Hecate, the Fates, or the Norns of Norse mythology. They classically appear in the persons of Maiden, Mother, and Crone, but just as often are of an age. Examples include Granny Weatherwax, Nanny Ogg and Magrat Garlick in Terry Pratchett's Discworld books; Orwen, Orgoch, and Orddu in Lloyd Alexander's Prydain books, and Mildred, Mordred, and Cynthia in Neil Gaiman's Sandman graphic novels, down to the Sanderson sisters in Hocus Pocus. The most famous three, of course, appear in Shakespeare's Macbeth.
The Witch Queen. The Witch Queen (who is not necessarily the Queen of the Witches) is a master of deception. She disguises her malicious actions behind a beautiful exterior, but she can use her position to help work her will. The Queen in "Snow White" leaps to mind right away. The White Witch in C. S. Lewis' Narnia books, the Queen in Terry Gilliam's The Brothers Grimm, and to a lesser degree L. Frank Baum's Queen Zixi if Ix. The Witch Queen might actually be a crone made beautiful by her glamorous magic.
The Good Witch. Good witches are (or were, perhaps, until recently) statistically rarer. If there was a good female magic user in a tale she was more often referred to as a wise woman or perhaps a fairy godmother as being a less opprobrious term. Glinda the Good Witch of the South in L. Frank Baum's Oz books is perhaps the most familiar example of this type, and indeed in the 1939 movie she resembles a good fairy more than the usual idea of a witch. Zaneba is the good sister of the evil witch Yubaba in Spirited Away, Princess Irene's "Grandmother" first appears as an aged crone in George Macdonald's The Princess and the Goblin, and almost all of Terry Pratchett's witches are good. The odd thing about good witches is that they can be almost as intimidating in their pursuit of good as bad witches in their pursuit of evil.
The Witch-In-Training. This type of witch is a fairly recent development. While a full-fledged experienced witch might actually be too powerful to figure as an interesting main character, one who is just learning is hindered from solving her problems too easily and is naive enough about the magical world to act as a reader's stand in. As the witch learns, so does the reader. This type is most often a little girl. Judy in Camilla Fegan's Late For Halloween, girls in Ruth Chew books like The Wednesday Witch and The Witch's Buttons, and lately and perhaps most greatly Tiffany Aching in Terry Pratchett's books. Miss Price in Mary Norton's Bed-knob and Broomstick is a grown-up example; she only takes to witchcraft late in life.
The Modern Witch. The epitome of the modern witch has to be Samantha Stevens and her family from the TV show Bewitched. The modern witch is miles away from pointy hats or eating children; they dress ordinarily, try to fit in, but can be a little "kooky" or bohemian around the edges. At some point a story about a modern witch will almost certainly have someone riding a vacuum cleaner. Besides Bewitched, the movie Bell, Book, and Candle, Peggy Bacon's "About The Good American Witch", and Margaret Embry's "Blanche's High-Flying Halloween" are good examples of the modern witch.
These are, of course, very generalized types, and any given witch might wander between them. There are almost as many types of witches as there are authors who write about them. But you can point to any one of them and say "That's a witch, all right."