From my studies, I've found that the chakras are a western addition to the reiki practice; probably due to the majority of western energy workers being set in the chakra paradigm. However, this paradigm of energy comes from India and the Hindu religion: yogism, tantrism, vedism, brahmism. You would learn them more correctly from studying those modalities with their esoteric beliefs.
Although, my best advice is to let them activate themselves as you increase your consciousness and awareness through through energy work--of which, reiki is one modality. Healing energy work is what you should focus on; for some reason, many people who have used other types of energy work or had someone supposedly o"open " the chakras for them also enecountered distressing side-effects.
In other words, do not get caught up with all the hype about chakras--it is bad practice. As you increase your awareness/conciousness any chakras you have will activate in a healthy fashion. Think about the goal: it is to raise your concsiousness and heal yourself, or heal yourself and raise your consiousness. As you do this, the abilities you seek from "opening your chakras" will come without distortion.
The increase in abilities you seek is only an enticement to raise your conciousness, if you make those abilities or chakras the goal, then they become nothing but a distraction from the...true "light" as they say.
**Otherwise, ask at the reiki energy board you are talking about.
