It can be a difficult read, particularly if you don't have a full grasp of the context. I would recommend that you read Marx's writings on the Civil War in France if you haven't already. It outlines the historical process that Marx saw unfold, particularly in the Paris Commune, which led him to believe that a Dictatorship of the Proletariat would be necessary before a full transition to communism.

Essentially, like the poster said above, you will need to have a force (e.g. dictatorship of proletariat) that is capable of repressing the bourgeoisie and all other forces of reaction after you have won the first stage of the revolution, whatever that looks like (history doesn't always play out how we expect it to, as Marx noted) because if you DON'T have a force capable of suppressing them then they will reorganize, consolidate their forces, launch a counter revolution, and smash you. Marx saw this play out in the Paris Commune in 1971 - the brave workers of Paris established what was arguably the very first workers state, but because they were isolated, and because they didn't suppress the old figures of the ruling class, those forces were able to recover and wipe out the revolution in Paris, killing tens of thousands of revolutionaries.