To get you started on the right foot for the demo.
General tips: Read well the control guides for common controlls and the weapon of your choice. There are two methods for controlling the camera tapping L-trigger frequently to reset the camera behind you, or using the D-pad to manualy move the camera. If you choose the second option try holding the PSP so that your thumb is on the analogue and your index finger lines up horizontally accross the D-pad with the other three fingers holding underneath. This allows you to press left and right on the D-pad without having to loose control of your characters movement. Using O (while weapon sheethed) near low ledges, vines or walls with obvious hand holds will allow you to climb. Pressing O whith your weapon sheethed allows you to search the enviornment and slain foes for usable items. Opening up your inventory through the start menu allows you to combine items. The most useful early on is Herbs+Blue_Mushrooms=Potion. Holding L-trigger (during the regular mode not while in the start menu) will open up a quick inventory menu which will allow you to choose which item is in your quick item slot (square button). You can also change the type of ammunition you have chosen for your cross bows from this menu.
Hunting Tips: At your base camp there are two boxes, one red, the other blue. Always inspect the blue box (O) which contains free items that you can use during your quest (maps, potions food etc). The red box is a drop box for dropping off requested items and bonus items (worth cash but no other use). The creature you are hunting will roam until you engage it. Big critters hit hard. Learn to dodge (X) and watch his attack animations. Some of his attacks will leave him more vulnerable to counterattacks. When you have hurt it badly it will run away. Use a paiint ball before you think it will leave so you can track its movements. The creatures in the demo might be permanantly marked with a paint ball. I can't rember. When the creature is close to death it will run away to its lair to sleep, hopefully you have painted him or you already know where his lair is. There is a creature animation that lets you know that a creature is trapable which is different for each creature. Learning to recognize a creatures close to death animation can make trapping easier. If the creature is not close to death then a trap will only temporarly imobalize the creature - giving you some free attacks. Not every quest requires you to trap. Some can be completed by either killing or trapping. If you do trap you get more/better creature parts for upgrading your weapons/armor.
Ok, well while people are being helpfull and nice, I found these links invaluable when I first started:
That's all the Freedom Unite faqs out there. (Most of the Monster Hunter Freedom 2 FAQs are also current, it's basically the same game with a few extras)
This is one of the best 'walkthroughs' and by walkthrough I mean something that will set you up in the right direction and demystify most of the stuff that's going to confuse you.
This is the monster hunter wiki: http://monsterhunter.wikia.com/wiki/Monster_Hunter
It's great for looking up items and gear. Use the search, it works well.
Lastly, this is a wiki created by Capcom: http://www.encyclopedia-gigantica.com/
I find the previous link better, but this can have some useful stuff.
If you have questions about the game, check out the capcom forums: http://www.capcom-unity.com/monster_hunter/go/foru
Also feel free to drop me a message on here if you want to ask a newbie question about the game.