The crafting skill is in the skill tree. It's at the bottom and it has 3 tiers (for up to +30% chance to craft). It is VERY useful to max this out before you craft anything with less than 100% chance to craft, or you might lose your mats when crafting.
When you craft something and you don't have the required amount of mats, it will give you the option to purchase the missing mats for gems. You don't have to purchase them with gems, though. Instead you can just wait until you have all the required mats.
After you hit level 4, when the match is over, there will be a slider on the screen that shows the xp/gold/mats you got for the match so you can choose if you want more xp or more gold.
