Artifice is the art of magical item creation. Beyond the ability to channel magical energy, it requires an extensive knowledge of magical theory, alchemy, and crystallography. Most such projects also require knowledge of metallurgy, metalworking, woodworking, etc.
In order to craft magic into an object, you need a formula. Formulae are detailed designs and instruction sets which tell the artisan in minute detail exactly what is required to build the item in question: materials of specific quality or purity, specialized tools, temperatures, specialized spells, etc. Formulae are rare and precious; the cost of relatively common formulae like the recipe for a common healing potion might cost ten times the market price of the end product, and designs for particularly rare or powerful objects are typically not available at any price.
Once you have obtained a formula, you need appropriate equipment and raw materials. An artificer’s workshop is an incredibly expensive thing to build even before the cost of the crafting materials; most artificers work for a patron, usually a government but occasionally a very wealthy individual. Additionally, some crafting materials are not available for purchase due to rarity or laws forbidding possession.
Finally, you need a power source. Lesser items can be crafted in a few weeks or months, but more powerful items typically take the efforts of multiple casters over a period of years. This is because the sheer amount of energy required is much more than any spellcaster can handle safely; it must be fed into the item at a carefully measured pace. Stories abound of artificers who took shortcuts and turned their workshops into smoking craters, usually devastating a good chunk of the local countryside at the same time. The more energy an item has been charged with when something goes wrong, the larger the explosion.
As the amount of energy which can be safely channeled into an object is limited within a given time frame, and as greater amounts of energy carry greater risk should something go wrong, there’s a practical upper limit on the power of a crafted object. Some say the duergar have found ways to circumvent this limitation, and the Dragonborn are rumored to be doing research into the subject.