Hi Bro
Can you edit your Thread Title "Who knows?" to something better and I am sure is your intention = something like "Beginner Game FAQ" or "Game Basics". Top Game experts are mainly discussing in Discord channel so this forum is a little lackluster and neglected it seems.
Items are like in any other game = one time consumption resource that gives different benefit. There is no Slot limitation like as with Tower chest slots. Just click on a item to know its use.
To unlock a New Girl, lesser rarity girls (Common, Rare and Epic), you have 5% chance while opening Wooden shop chest (Free, with Timer of 4hours). Other chests for higher rarity girls, Silver Chest (Legendary) and Gold chest (Mythic) -> can be opened by using Gems. Note that item Key (Bronze/Silver Key = reward from Colosseum Event) can open such Shop chests instantly - BUT it should preferably be reserved for game event goals. Also, from my personal game experience, you have more likely to unlock a Girl when opening chest during Game event. A game event in the Past ="Pussy Market", lets you unlock a new girl for certain number of coins (soon a new event will replace it). Note that Any girl can be purchased from Shop with Money.
"Packs" are very helpful for any Player as it lets you choose a girl you from different number of options , with sometimes a chance to get a 'New Girl' unlocked as well as get good numbers of it. Infact, the number of girls have been doubled from previously, 1750 girl cards from Common Pack instead of 875. sometimes, on a lucky super roll, you can pick to get even higher number of cards.