Why it exists. To say that someone or something has two qualities at the same time: "both … and …". Lisa says it about takeaway in Text 3: 外卖又快又方便wàimài yòu kuài yòu fāngbiàn.

Person / thing又adjective 1又adjective 2

+这个房间又大又干净。Zhège fángjiān yòu dà yòu gānjìng.This room is big and clean.

+那家店的衣服又好看又便宜。Nà jiā diàn de yīfu yòu hǎokàn yòu piányi.The clothes in that shop look nice and they're cheap.

+那家饭馆的菜又贵又不好吃。Nà jiā fànguǎn de cài yòu guì yòu bù hǎochī.That restaurant's food is expensive and not very good.

+她说得又快又清楚。Tā shuō de yòu kuài yòu qīngchu.She speaks fast and clearly.

Key points

Usually both sides point the same way: two good things (又快又方便yòu kuài yòu fāngbiàn) or two bad things (又贵又不好吃yòu guì yòu bù hǎochī). For one good and one bad, use 可是kěshì: 这个菜很好吃，可是有点儿贵zhège cài hěn hǎochī, kěshì yǒudiǎnr guì.
Usually no 很hěn after 又yòu: say 又快又方便yòu kuài yòu fāngbiàn, not 又很快又很方便yòu hěn kuài yòu hěn fāngbiàn.
After 得de too: 她说得又快又清楚tā shuō de yòu kuài yòu qīngchu, 他写得又快又好tā xiě de yòu kuài yòu hǎo.
Not in the book · it also joins actions: 孩子们又唱又跳háizimen yòu chàng yòu tiào "the kids were singing and dancing".

Common mistakes这个菜又好吃又贵。 → 这个菜很好吃，可是有点儿贵。Zhège cài hěn hǎochī, kěshì yǒudiǎnr guì. One good and one bad sounds odd with 又……又……yòu… yòu…: use 可是kěshì.
外卖又很快又很方便。 → 外卖又快又方便。Wàimài yòu kuài yòu fāngbiàn. Drop 很hěn after 又yòu.
我又饿和又渴。 → 我又饿又渴。Wǒ yòu è yòu kě. No 和hé between them.