CS2 skins by source
Operations, the weekly drop pool and souvenir packages. Cases have their own section.
Operations Collections added with CS operations; many can no longer drop and only get scarcer over time. 
Cases Skins from weapon cases opened with keys — the main source of Covert designs, knives and gloves. 
Weekly drops The active drop pool: collections you can still earn from weekly care packages after matches. 
Souvenirs Souvenir packages dropped during Majors: skins with gold event stickers from the maps being played.