Crafting is an important aspect of the game, with which everyone will meet sooner or later. It is very simple and intuitive. Your character knows all recipes from the beginning of the game, only limitation is the need for having the right level and required resources.
There are two ways to gain access to the crafting menu. To use alchemy, cooking or scroll-making, you must enter your equipment and then click the crafting icon in the lower part of the window. To use enchanting, you must click the right mouse button on an item. In the newly opened window you can read item description and check its stats, and in the lower part there is an enchanting button that moves you to a separate menu.
Some item require a lot of gold for creating as well.
Alchemy gives you access to dozens of recipes. Best option is to create potions just before facing an enemy you have trouble defeating. If, for example, you're fighting a dragon, create some potions that improve your elemental resistance. Each of your characters should have at least one potion with them that immediately recover some endurance. Remember, that alchemy is relatively cheap.
Cooking creates food that gives bonuses to various parameters (mostly endurance). To create food, you don't need gold, only resources. Food is very useful for characters that use melee combat, so try to ensure that they will always have access to it. Instead of cooking yourself, you can buy food in nearby tavern as well.
Crafting scrolls become very important on higher difficulty levels, when spells that your magic characters have are no longer enough. Thanks to scrolls your priest can cast powerful offensive spells, and wizard will heal your companions. Remember, that high lore level is required to use a scroll.
Enchanting is probably the most important type of crafting. It allows you to greatly improve your equipment stats, and thus your character. You must remember few things when enchanting. You can enchant only weapon and armor. Up to three effects can be enchanted into one item. You should enchant only those items that you are sure you will be using for long time. In case of warriors it is best to improve overall armor quality. In case of weapons add secondary damage. As for magic classes, you should add some stat bonuses to armor, like to intellect.