i dont understand what Mccarthyism is?

i dont understand what Mccarthyism is?
im supposed to write a 3 page essay discussing the advantages and disadvanages of living during the Mccarthy era; the thing is, i do not understand what it is at all. can anyone describe to me what it is exactly and help give some advantages and disadvantages. wikipedia and other internet sources arent helping me at all :[

Mccarthy told the press he had a list of communists who held political power in the US in the 1940s. The people were so afraid of communism thanks to the indoctrination from our schools that they supported Mccarthy. There is not advantage to it unless you are the person lying and playing off peoples fears. The disadvantage is making outrageous claims like “the Jews caused Germany to lose WW1” and “atheists are devil worshipers” which leads to the Holocaust and Inquisition respectively. The person lying and working up the mob gets power until people stop acting so retarded and realize the big mistake they made. Usually it’s too late.