HO's are started by doing spells/abilities in a certain order - as stipulated by some little pictures that come up in fights.
First you must start combat before you can launch an HO. My druid either gets close to a target and melees or pulls with his cold damage spell (so his HO spells will be fresh).
Once combat is engaged push your HO-starting spell/ability (which you get automatically at lvl 5 or so). I forget what my druid one is called, but it's obvious what it is when u get it (about lvl 5).
This one almost always executes fine - and you get a little picture-thingie. Now you're half-way through the HO starting process - and the next step is to get to the "wheel".
If you are a priest it shows a "green coin" and a "little hammer". The coin allows a scout you might be teamed with to click one of his coin abilities and change the HO. So if yer a soloin priest, ignore it. Focus instead on the little hammer. If you fire off the spell that the hammer signals, you advance to the next step of the HO, which is the Wheel.
That means Smite. Why? "Examine" your smite spell, and you'll see it has a secondary icon associated w/ it for HO purposes - the little hammer.
Okay, if the smite isn't interrupted, you advance to the next step - the wheel. In the case of a priest, all he has to do is cast ANOTHER smite (it's the only icon on his wheel). And bam, the HO goes off. It always seems to give extra damage (my smite does 30-40 at lvl 13, if I remember right, and the HO does the same or a bit more). Oh note, my Smite is upgraded to apprentice lvl 3 ... a whole new dimension of complexity - look up apprentice and adept levels on other threads - you also need to know this.
Once the HO goes off the wheel vanishes. You get a message that it did something. ANd you can start it again.
My new scout, who is lvl 6 on IoR, solos really well and gets two HOs off a fight regularly. He starts w/ ... bah, I can't remember what it is called, but it's a flank/back attack that does lots of damage. I sneak first if I'm taking on an a mob that isn't indifferent, then hit it w/ this flank attack. Once melee is engaged, I start the HO (lucky break, I think) - then Evade, which brings up the wheel - then Quick Strike - which makes the HO work (it does extra damage and sometimes buffs me). Two-three seconds after the first HO goes off, Lucky Br is ready to fire again - but now Evade is resetting on a long timer and not usable. So I use my lvl 6 ability, which is something like Dirty Blow - or ... it stuns - but mostly it ALSO moves the HO to the wheel phase (it has the same HO symbol/icon as Evade) - and then the wheel is back up, asking for Quick Strike. It recycles fast - you only have to wait about 2 or 3 seconds for it to work. And wham - when it goes off - your mob is either dead or near dead. My lvl 6 scout easily kills blue+ mobs like the skels and gob protectors (note blue+ means it cons blue but has one up arrow, which means it is much tougher than a normal blue mob - more like a yellow - why? heheheheheheh, I have no idea!).
Fighters engage combat, start HO, hit Quick Attack to get wheel, - and then strangely hit Taunt to finish the HO (a horn) -- and they usually get a big damage hit on the target and sometimes a buff.
I forget what mages do soloing, but it's similar and easy.
NOW that's soloing. Grouping, I've read, can yield "cross class HO's" which are muuuch more powerful. Plus I've rarely seen em go off in groups - once in the cave an area blast knocked over 3 ratmen - wham. But I'm still working on the nuances of getting these off. They seem to work much like the solo ones - but mostly u must get a system in the gruop so that when one guy starts the HO chain - other players *don't break it*. See, if the chain comes up - the starter picture before the wheel - the *next* spell or ability used, if it matches one of the symbols, will move to the wheel --- but if you cast something that doesn't match it kills the HO. ANd you have to start over.
Oh, on cross-class group HOs, you get more than one symbol to match on the wheel. ANd it seems once the wheel goes up that it doesn't get broken by a "mismatched cast" - it just waits till each symbol gets matched in order. Once I saw the wheel go when I was grouped - there were three symbols - a scout one, which he did - then a sword - which the tank did - and we were down to one symbol - a moon. Then it hit me the moon was a priest one (I was playin my druid) - it's my SEcOND heal spell - and even though the tank was barely hurt I healed him w/ the moon one - and WHAM - a big area nuke went off. It was cool.
I've yet to see this in the game - but smart people who post here say they do this to get group HOs off: they have the tank start, and wait for the healer to do the first heal. Healer has a button that says "heal done - start HO now!". Then a DESIGNATED Ho starter goes. No one hits a spell or ability til the wheel is up, unless he has to get the wheel up. The group will experiement - cuz one class might only ever start lame HOs while another does wicked area nukes.
Don't expect much success on group HOs yet - players are still pretty shocked that they have to learn this - and it only takes one "confused one" in the group to ***** it up (and hey, I'm not dissin anyone here - the "confused one" is often me!).
That's all I know. Hope I have it right. Check other threads and mostly practice HOs yourself on GREENS. Then go solo yellows. GL all!