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what does the colored bar by everyone mean? is it health?or something else and if its health then what the lowest and whats the highest?

Do you mean the bar you see ingame?
The left one shows your mana level. The right one is for your health.

If you're talking about the red, yellow or blue bar that eery char has:
This bar has no deeper use. It is just there for easier identification of single chars in larger groups. You can turn it off with F11