I don't know. What about it is confusing for you? You generally just have to click on the skills, and then can either click "learn" or "more info" on them. The skills underneath of numbers, like the Hail skill being under a blue 4, mean that you need 4 points in Ice skills before you can learn them.
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Well the first time you open the skill tree it explains how it works. I could add lines to make it look more like a skill tree but that would imply you have to get certain skills in an element to unlock other skills, when all that matters is enough points in an element, so i don't think that really helps.