If you want a good introduction for how Marxist's understand what separates their form of revolutionary socialism from all others, this is the book to read.

Utopian Socialism is an old and hallowed tradition, but one that does not seem to have had much lasting impact in the western world. Scientific Socialism - Marxism - is an attempt to understand the process of history and use it to the ends of human emancipation. Engels here goes into great depth on the differences between the two, it is not a long read. Would recommend!