Anarchists have significant differences with Karl Marx and many marxists, (especially of the leninist tradition) in both theory and organisation. However, Bakunin and many other Anarchists recognised the contribution of Marx in his ‘Critique of Political Economy’. It is a tool of the working class to critique capitalism, and to analyse class composition for future struggles. Here are the pdfs available of his major works, (Michael Heinrich’s introduction is a good place to start):
heinrich-michael-an-introduction-to-the-three-volumes-of-karl-marxs-capital
Capital – (Penguin Classics) Volume II
Capital – (Penguin Classics) Volume III