ELO?

Whats ELO used for? i know i earn ELO from duels but what is the use of it?

Its used to determine who is more competent in 1v1 games ...but its not totaly punctual.

Ok what if i lost all my ELO will i be able to duel? and thnx for the answer

It is impossible to run out of ELO rating, If your rating is lower than your opponents you will not lose as much ELO but you can gain a lot.
If your rating is higher then you have less to gain but the price for losing is higher. The lower your rating the slower you will lose ELO.