OK. I am new to the series and just spent about 30 minutes on the demo. This is what I need to know:

How the heck do you even play? I just spent 30 minutes slashing the level 1 Great Jaggi with no results.

There isn't even a tutorial to tell you what to do or how to play the game. So, I know what my health and stamina bar is, and that is it. There is some other short bar underneath it (weapon health?) and yet another bar underneath that. The bottom bar seems to fill when you hit the monster? Then there is something that looks like a thermometer on the left. I know what the health and stamina bars are but not these other three.

I slash at the Jaggi, the bottom red bar increases...I think. I don't know what that means (number of hits?). The Jaggi won't die. Does IT have a health bar? Where is it? Do I have to hit it with a 50-string combo without breaking to kill it? Do I have to kill all the little monsters first? 

There are not really any instructions. The Jaggi falls over occasionally, but gets up again. Do I pull a lasso out of my pouch and string him up? Once again, no instructions.

Shouldn't a demo have a tutorial or at least tell you how to play the game? Not just here is a game, play it. For all i know you have to hit up, up, down, down, left, right, left, right, B, A when the monster falls down to finish it.

Just keep attacking until the bastard is dead, the MH games have a tutorial to give you the basics so don't worry. The weapon bar indicates weapon sharpness as you attack it changes colour telling you it's getting blunt, you deal with this by using a whet stone to sharpen it as sharper weapons deal more damage, haven't played the demo as we don't get it in Europe but I assume by you saying the other bar that you were using long swords (Katanas), they have a dark release ability which fills up as you attack when full you activate it and it boosts attack power and allows a continuous combo until the bar depletes.

yea, I was using long sword. this is a bitch for a level one monster. when the monster runs away does it heal?

In some cases yes but only if you don't find them quick enough as most will find a place to sleep to heal up so if he's sleeping when you catch him he would of healed up a bit but don't worry too much if you're having trouble as every MH fan you see was in the same situation you're in, trust me it's a long hard lesson for all of us, with the full game I'll just advise on spending time on it to hone your skill and you'll get there, can't comment on the demo but in the MH games numerous monsters make a break for it when they're getting thrashed so if he's running it means you're causing him problems. To deal with running monsters hit them with a paint ball so when they run they show up on your map, sometimes people track the creature down mainly bigger targets and wait for them to start sleeping then the attack.

I see. This game seems to automatically track the monsters on the mini-map. so no problem there. maybe i'll give it another go after work since now I know there is nothing special that has to be done.

how often are you getting hit?