It's a description of one possibility of how a cloud of gas & dust can congeal into a star with a solar system.
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I would agree with quantumc but would point out that gas and dust have a mean free path that causes the gas to stop relative motion within the cloud and precipitate the collapse. Ultimately random motions cancel out but there is almost always some angular momentum that shows up as a net and this is what forms the planetary accretion disc. The greater the net angular momentum, the larger the ratio of total planetary mass to stellar mass that star system will have. No net angular momentum would result in a total collapse with no planets and a high net angular momentum would result in a super system with primary and secondary orbital systems like ours and even tertiary systems with orbiting secondary stars having planets and moons. Aliu Sage