Leftists are not liberal; the two are diametrically opposed to each other. (Right-wingers are similarly opposed to liberals, just in a different way.)

Liberalism favors democracy, rule of law, freedom of things like speech, free trade, free-market economics to various extents, etc. Leftists oppose much of this. If you want to see what leftists support, just read about the history of the Soviet Union. (And if you want to see what the right-wingers support, read about the history of Nazi Germany.)