Well, the main one is that communists/MLs believe that you must first form a communist state to combat capitalist states and capitalism before transitioning to the ideal classless, stateless society. Anarchists believe that the destruction of the state must occur concurrently or even before the destruction of capitalism.

Like the other person said, the main divide is the usage of the state and "authoritarian measures" as need arises, Marxists will use the means required to face threats even if its not ideal or perfectly moral, Anarchists will either idealistically avoid any such measures and get crushed, or implement mutated versions of the same measures while insisting its nothing alike, like with Makhnovia and Anarchist Spain.