Prana, Reiki, Chi, ... They are all different names for life energy. Just like the universe is made up of energy, so are you.
Your physical body collects energy from oxygen, food & sleep. These are conscious forms of energy.

When we look a level deeper we can see that there are also unconscious forms of energy at play.
Think of your heart that pumps your blood, your intestines that digest food & your lungs that take in & distribute oxygen. This is not something you do consciously but it all happens automatically...

All of this is controlled by something else, something a lot more subtle...

You can already guess, this is the life energy. This flows through all you can see, hear and can touch. It moves through all & makes everything move...

That life energy flows in & around your body as well! Just like blood flows through the bloodstream, there are also different channels that this energy flows through.

Where various of those channels meet you find energycenters or chakra's. They are located around important organs or glands, there is also an interaction between the body and the chakra's.

Your emotions and thoughts can also influence the energy (and also the chakras) in your body & vice versa.

When your energy is unbalanced and doesn't flow well you will feel bad, you're more vulnerable for diseases and you have less capacity  to deal with life.

This also works the other way. When you're stuck in a negative thought pattern, are sick of have experienced trauma this will influence your energy system.

You might remember having been in a bad situation or that you feel 'bad vibes' from a person, what makes you feel bad.

This means that your gut feeling (solar plexus chakra) is telling you that something isn't flowing with your energy.

But there's also positive influences! Think about being in love (heart chakra) or having an openhearted converstation with someone (throat chakra). All the stuff that makes you feel good & 'in the flow'.