I need help with Oro's Sacrifice

I get a Frenzy Charge if i kill a monster with just one attack hit(with 100% change to ignite)?

I mean, i just need to ignite right? The ignite does not need to do damage.

"Gain a Frenzy Charge if an Attack Ignites an Enemy"

So, yes, all you need to do for the Frenzy Charge to pop in is to deal a Ignite with an attack. What's more, it will also count Ignites on already-ignited enemies, since it does not specifically say "Ignites a non-Ignited enemy".

That said, you still have to proc the ignite somehow. In order to do so, usually you just need to inflict damage while having a chance to Ignite, or just crit right away which will always proc an ignite.

Usually, this means that as long you have at least 1-1 Fire Damage (which Oro amply provides right away by itself) and have a minimum +x% Chance to Ignite, you will apply an ignite on enemies (unless you are using that Oro with a Elemental Focus, or you are using something that does not allow you to deal ignites or elemental ailments in general, for example by equipping a The Three Dragon without adding some Cold Damage to your attacks).

Bear also in mind that if you convert somehow all your Fire Damage to another element(s), thus having a 0-0 Fire damage, you will still be able to deal ignites if you allow at least one of those element to Ignite (should be quite hard if not impossible since the only thing you can convert Fire is into Chaos, and The Infernal Mantle does not provide a 100% conversion)

Finally, If you attack hits more than one enemy (which is something even a Flicker Strike sometimes do), you will still only gain one frenzy charge if at least one of them gets ignited.

Hey, thank you so much, this helped a lot.