What exercises can I do to boost my general level of energy? Thanks.

The first thing that comes to my mind is anything. Which is good! What do you enjoy? I think anything that gets the heart pumping is energizing and anything that builds muscle makes it easier to do general tasks, like getting up from the couch, going up stairs or lugging in groceries. So I think anything would be good.

What do you enjoy? Tennis? Biking? Walking? Swimming? Hiking? Ball exercise?

I personally find the most energy from doing interval training. That's where you do something of a higher intensity for a small amount of time, like two minutes, and then you do two minutes of less intense training and so on until you've reached your goal of 12, 20, 40 minutes. This could be walking up a big hill for two minutes, turning around and walking down for two minutes, then back up again. Or if you're using a machine, there are often settings for it. On a treadmill you'd increase the incline and speed for two minutes, the decrease for two minutes.

I do high intensity intervals, so I run up and down my stairs as fast I can for 30 seconds then walk for 90 seconds and so on.

I will go with anything as well.

My mom used to complain a lot about lack of energy but then she bought a gazelle and started doing it. She does about an hour every night and overall says she feels less tired throughout the day.

For me, when I am doing a regular exercise program, I feel lots more energy. I do weights and cardio.