The rounds system is designed for a gamified quiz that needs a combined leaderboard (also called ranking) over multiple quizzes in time. For example this is used on events where there’s a quiz with two rounds: day 1 and day 2. And the winner is the one who scored the best in both quizzes combined.
Now for what the system does:
A round is only available during a certain period in time. If a round is not yet active, it will show a timer/countdown untill the next round. For every round the system will select an X number of questions from the total amount of questions the quiz has. At the end it will show a leaderboard for that quiz and people are also able to look at the combined leaderboard.
It really depends on your use case if the rounds feature is the best feature to use. Other possibilities are using our courses section, or creating multiple quizzes.