If you can lift the weight more than 12 times, you need something heavier. If you can't lift it at least 8 times, you need a lighter weight. Doing 8-12 repetitions is called a set. I recommend that beginners do one or two sets. Work the large muscles first.
Small muscles fatigue quickly.
When they get exhausted they can't assist the large muscles. This sounds silly, but beginners often hold their breath during lifting, which can cause a sharp rise in blood pressure. Wait 48 hours between sessions. Muscles taxed by weight lifting need about 48 hours to repair. You must give your muscles time to recover so that you get the fat burning benefits.