So how exactly do a get seals?

I just picked my Grand Company and am fiddle-farting about doing quests for them and whatnot and am noticing I am gathering seals for them I know if I do the crafting missions for them I can get seals that way, but out about in the world how am I getting them? Is it through quest completion or killing mobs or a combination of the two by chance?

Grind FATE's.

I think the fastest way is doing fates, I got like 5000 after like an hour or two without realizing it. Fate grind

GC Hunting Log & FATE's mostly.

Far out thank you