The first chapter of Capital is the hardest one. This puts a lot of people off because they are used to expositions arranged in ascending order of difficulty. But Marx had a good reason for writing Capital the way he did. Before he could talk about surplus value (i.e. how capitalism exploits the worker) he had first to say what value is. There can be no surplus value until labor power has become a commodity, bearing value. But Marx's theory of value, upon which all his subsequent conclusions depend, is the one that most readers (especially Anglo-Saxon ones, including the author of many a written comentary) have the greatest difficulty getting their minds around. The commentary that helped me most is "Essays on Marx's Theory of Value" by the Soviet author I. I. Rubin (liquidated by Stalin), together with Fredy Perlman's introduction.
Jim