The man who had some medical condition for 38 years got healed and carried his bed home. It took place on the Sabbath, and it raised some eyebrows.
The Jewish leaders interrogated the man because man carried his bed on the Sabbath, which breaks the rules (5:10). It's worth noting that while the Jewish leaders may point out phrases that may say "no carrying", the context and point of Sabbath is making sure that people don't do jobs and rest, and carrying the bed is not a job that the man does for a living. Anyway, in response, the man replied that someone healed him and told him to get up and walk -- though he did not know who the healer was since Jesus moved away from the crowd for some matters.
Eventually, Jesus returned to the man to reveal himself. Jesus also said to the man to "stop sinning" in order to prevent "something worse from happening" (5:14). Jesus made the comment because sin by itself ruins lives. God does not like sin not just because it breaks God's rules; sin ruins relationships with other people and can sometimes ruin our lives too.
Now that the healed man knew who the healer was, the healed man responded to the Jewish leaders that Jesus healed him. The new information provided led into more dialogue about Jesus.