There is often some confusion about which is which and whether they are somehow symbols of "evil".
The " Pentagram" is any five-pointed star. It can have regularly shaped arms or it can be irregular. There is some good information about it at https://www.mathsisfun.com/geometry/pentagram.html
The "Pentacle " is a Pentagram contained within a circle.
Although both the Pentagram and the Pentacle are now largely associated with Witches and with Satanists, this has not always been the case. In Jewish mysticism the Pentagram is seen within the Kaballistic Tree of Live. And in early Christianity the Pentacle symbolized the 5 wounds of Christ held within the crown of thorns, while the Pentagram represented the star that led the Wise Men to Jesus. In Chinese thought, the Pentagram represents the Five Elements (Earth, Air, Fire, Water, and Metal)
During the 14th and 15th century, the Pentagram and the Pentacle were adopted by Ceremonial Magicians who drew heavily on both Kaballistic and Christian thought and symbols in their magical workings. When such practices were deemed heretical by the Church, the Petagram and the Pentacle were seen as being "evil" and their prior association with Judaism and Christianity were forgotten.
With the resurgence of interest in magic in the 20th century, both the Pentagram and the Pentacle were adopted by various magical groups such as Witches, Wiccans, and Satanists. In Wicca, for instance, the Pentacle represents the Four Elements within the circle of Creation.
Satanists (at least some of them) see it as representing Baphomet and draw it inverted (single point facing downwards) and with a goat's head superimposed on top of it.
Because Satanists use the inverted Pentacle, this particular symbol has taken on an aura of being somehow "evil" . This isn't necessarily the case. For instance, in some Traditions of Wicca the inverted Pentacle or Pentagram represents the 2nd Degree initiation.
I hope this clears up some confusion over the Pentagram and Pentacle. And I hope it helps to see that a symbol can have many different meanings depending on the culture and context within which it is used.