Charity Corner (CC) its an event where "Granny" needs you do donate item for her. First time it was introduced (2014) they chose categories for the items you could donate, you would donate 5 items from that category and and you would receive in exchange an item between the total range. So for example, if the category is Toy and you donate 5 r70 items, you would get an item ranging from r70-79. Same goes with r80 and r90. Nowadays instead of getting an item you get points, that you later can exchange for perks, detailed in the perk shop.
And yes, basically you save junk items, preferably from the r90+.