The creation of a magical item is an intense process. It can take years to accomplish and is potentially deadly. The steps are as follows:
Decide on a purpose for the item that you want to create. The more vague and the more in-character this purpose is, the better your result will be.
Decide on a patron for the creation of the item. This would be a god, a demon lord, a fey queen, or some similarly powerful non-mortal entity. The more fitting the entity to the item and the more powerful your patron, the better your result will be.
Determine a means to contact your patron. It may be as simple as walking into their church, or as complex as a planar quest. More direct methods of contact will yield a better result.
Determine an offering to your patron. For your patron to hear your request, you must offer them something. This offering need not be a physical thing. The more valuable your offering and better it fits the patron, the better your result will be.
Determine a deed for your patron to bless. The creation of a magical item occurs when a worthy deed is blessed by a powerful patron. The greater the deed and the better it fits the patron and item, the better your result will be. Make your deed specific and measurable.
Contact your patron. Fulfill whatever action you need to take to contact your patron.
Offer your offering to your patron. If your offering is accepted, continue to the next step. If not, you will need to restart the process.
Ask your patron's blessing for your deed. If your deed is blessed, continue to the next step. If not, you will need to restart the process.
Complete your deed. If you succeed, you will gain your magical item. If you fail, you will need to restart the process.