The Wikipedia article for the attack has a pretty thorough summary of the events, most aspects of it are pretty well documented as far as I can tell. Essentially, the police were able to slow them down while congress members were evacuated to more secure areas. After a woman was shot breaking into a barricaded chamber door, much of the attack seemed to dissipate, and not long after further reinforcements were able to help clear the rest of the building. Trump then told his supporters to go home, knowing they had been routed.