Well, how to activate it? Actually, where are they located in our body?
Below is the picture that shows these energy points in our body.
Courtesy: Google Images
Reiki is the most popular and easy method to energize these chakras. Sound meditation is also a very effective method.
Color visualizing technique:
My husband is a Reiki. He explained to me once about the different colors of chakra and one way for a chakra meditation is to visualize those colors during chakra meditation.
Here is a real demo of chakra meditation in YouTube. Duration is 9 minutes.