To understand the distinction between the two systems, we have to understand the phrase “means of production.” Means of production are, simply put, the tools used to turn raw materials (some examples might be cotton, steel, or silicon) into commodities (clothing, car, computer chips, etc.).
In capitalism, these means are privately controlled, and are operated for the profits of the owners. Workers have no ownership, except in the rare case of worker-owned co-ops.
In communism, the means of production are controlled democratically by the workers; the people who perform labor own the tools they use to make commodities.