Training for weightlifting is done in sets. A set of 10 means that you lift and lower a heavy weight 10 times continuously before you rest. If you repeat these sets of 10 three times with a rest period between each set, you have done three sets of 10.
Most competitive bodybuilders spend hours trying to do many sets over and over again.
You don't have to do that. The reduced workload causes fewer injuries and leaves you with a lot of extra time to do other things. Lifting weights enlarges your muscles and makes you stronger, but it does not make you fit. Fitness refers to your heart and is gained by exercising continuously for several minutes by running, cycling, skating, dancing, walking, swimming and so forth. A complete program would include lifting weights twice a week and doing a continuous sport for 30 minutes three times a week.