Resources are used in Profession tasks for Alchemy, Artificing, Jewelcrafting, Leadership, Leatherworking, Mailsmithing, Platesmithing, Tailoring, Weaponsmithing, and Black Ice Shaping. (There are also resources used in Summer Provisioning and Simril Lightcrafting but they are seasonal items not used elsewhere.)
They are stored on a separate inventory tab so they do not take up regular inventory space. Resources generally stack in groups of 999, after which a new stack will be created and occupy a new slot in the resources tab.
Many resources can be used in more than one profession (uppercase X) while other resources are unique to a single profession (lowercase x). In addition to resources, some professions require consumables or other items in tasks, which are generally items that can be created in other tasks for that particular profession.
Resources can be found in a variety of ways. Some resources can only be bought from M'tari Prin'tal's store found in Protectors Enclave and Profession Resource Merchants found occasionally in special event areas. Most resources can be found in skill nodes, chests, or as loot drops from adventuring. Many professions have a gathering task which provide specific commonly used resources for that profession. Professions packs in the Zen Market provide a random assortment of resources. Certain epic level resources can only be found in specific locations in the game.
The following table shows which resources are used in each profession. Note that this table does not include consumables or other items that may be required for profession tasks.