It's a debuff like any other, so can get resisted depending on accuracy of the attacker and resistance of the target, at the time that it's being placed. But provided that it is successfully placed, it'll do a fixed amount of damage each turn until it expires, 3 percent of their health (though on Clan Boss it's capped much lower than that, with also a distinction between rare champions' HP burns doing less damage than epic or legendary ones). 

Ok, that clears that up then,, 

was noticing differences and it just didnt click what was going on