The Workshop in the Central Cinema is where you can synthesize new weapons, armor, and accessories using materials gathered from the labyrinths. Materials are obtained by defeating Shadows, collecting from 'Gathering Points' (sparkling spots on the map), and as rewards from quests. The quality and rarity of equipment you can synthesize depend on the materials you possess and your progress in the main story.
Regularly visit the Workshop to check for new synthesis options. Crafting new equipment is crucial for keeping your party strong and prepared for tougher challenges. Some rare materials are only dropped by specific F.O.E.s or bosses, so revisit areas if you need to farm for particular items. You can also sell excess materials for Yen, but be mindful not to sell anything you might need for a powerful piece of equipment later. The Workshop is your primary source of gear upgrades, so utilize it frequently.