The short version: don't bother with Arkhart.
The long version begins now: Arkhart is another incomplete game. They got the engine functioning, if not complete, but there's no real game here, and it's a bit annoying to toy with.
This is a 3D isometric RPG, which looks vaguely like Diablo would have if it had come out a few years earlier than it did. There's a backstory involving the arrival of some alien insects, and a rogue priest who starts a war between the 'humans' and the aliens, centuries ago, but in this demo sorta dealio, that doesn't really matter.
The biggest problem with this game is that it's not done, resulting in the main quest being about ten minutes long, and only that long because walking around is painfully slow and there isn't a run button. Outside of that, there are a few other things that make it not even as good as you would expect from that level of completion.
The developers were French, apparently. This results in the French equivalent of Engrish mostly, with some parts not translated at all, and therefore entirely inscrutable to my mostly monolingual self (I took Latin in high school, and German in college; I understand less than nothing of French). The font the game uses is a bit hard to read in the first place, and badly translated + badly rendered = hard to understand, if occasionally unintentionally amusing.
As far as I can tell, the only controls are the arrow keys, for rotating the camera and moving forward (you can't move backwards, which makes for an unintuitive experience from the getty-up), and the left mouse button for... clicking on things. Most things do nothing when clicked upon, but you can initiate conversations with NPCs via clicking on them, and I think clicking on a flower picks up some leaves of the flower, although I couldn't tell as the dialog box that comes up is entirely in French. I needed to collect two things, one of which I got from an NPC. I can only assume I got the other one from clicking on the flower.
The sound gets a little old (it's just one song that loops) but is nice enough. It has that fantasy film score vibe, only less so.
All you can do is talk to NPCs and walk around. I didn't do much exploration after it told me that I'd finished the demo, so there may be a massive world here, but if so, it's not worth your time to examine it. Which is a shame, because the graphics are crisp if a little old-school, the engine seems to work at rendering the environment, and with a little work it could have been used to build an actual decent game. I think.
But first they'd have to add a run key. The character walks at an amazingly slow rate; if they'd made the same game in the 2D tile-based Adonthell engine, it would have taken approximately a minute and a half to finish the quest, but it takes like ten or fifteen minutes here. The difference comes solely from the time it takes to walk from place to place.
Since this game hasn't been updated since 2003, I think it's safe to assume that you're really wasting your time if you bother downloading it. It's not a game, it's a tech-demo, and it's not even a particularly engaging tech-demo. If you're a member of the dev team that was putting it together, wasted countless hours making it work, and then somehow stopped before adding a plot or any real gameplay, I beg you to reconsider. It seems like you got the hardest part over; why not make something fun out of it?