This is walkthrough on the COMPOSE

The compose 4 stands for the number of times you can compose the item.
Requires level 6 means you need a character level of 6 to use the item.

[B]Weapon Combine[/B]
Fire + Fire = Fire
Water + Water = Ice
Water + Wind = Thunder
Earth + Wind = Poison
Fire + Earth = Attack Bonus (Static Value)
Fire + Wind = SP Recovery
Wind + Wind = HP Recovery
Earth + Water = Drop Rate
Earth + Earth = Critical Hit
Fire + Water = Attack Bonus (Percent Value)

[B]Armor Combine[/B]
Fire + Fire = SP Bonus
Water + Water = HP Bonus
Water + Wind = HP after kill
Fire + Wind = SP after kill
Fire + Earth = Block (Shield Only)
Earth + Wind = Defense Bonus (Percent Value)
Earth + Earth = Defense Bonus (Static Value)
Fire + Water = Magic Resistance
Wind + Wind = Critical Hit
Earth + Water = Drop Rate

[B]Accessories Combine[/B]
Fire + Fire = SP Recovery
Water + Water = HP Recovery
Wind + Wind = Critical Hit
Fire + Earth = Defense Bonus
Earth + Water = Drop Rate
Earth + Earth = Extra Weight
Fire + Water = Attack Bonus

Unless I mistyped something those should be the right combinations. Hope those help.

Also, as Hiroxi mentioned you have to go in order of level.
Lv. 1 = Small Crystals + Stone of Blessing (Purple)
Lv. 2 = Medium Crystals + Stone of Blessing (Purple)
Lv. 3 = Large Crystals + Stone of Soul (Pink)
Lv. 4 = Large Crystals + Stone of Holy (Orange)

Happy Combining!

As for leveling it's hard to say seeing as I've not had the chance to experiment with different builds. I personally use an axe, and the Hurricane skills. This in no way means it's the best. In fact I went with it, because historically these kinds of games tend to balance slow weapons poorly and I wanted a challenge. This actually worked out for me, though. The number of hits a skill does isn't determined by your weapon's speed, but its damage is. This means with an axe your skills will deal more damage. Again, this doesn't mean the axe is better than the other weapons. It simply means that your skills will deal more damage with an axe.

In my limited experience the best thing you can do for yourself is make a few items with +drop rate, +critical hit, and +hp/sp regeneration. I'm currently running with 44% crit, and I've added no points in Luck (except from the talent that gives +5 all stats). My gear gives me 36% crit right now. Crits do double damage, so it helps a lot.

With +drop rate gear you'll find lots of gold, and items you can vendor. This makes everything else much easier. Particularly buying items from Chung. Chung's items come with precombined stats on them, but still have all their combines so you can add even more. Additionally, the price for the item is actually cheaper than it'd take you to do it if you bought all the crystals/stones yourself so it's a good deal.
Likwid game the best :)