Translation:That bed is big.
As a Japanese person this confuses me too, they don't exactly make the same sound, in 「おう」 it's more like an "o" fading into a "u" and in 「おお」it sounds like you went to a middle school and you hear some teens yelling "OOO". I honestly prefer writing 「おう」as "ou" and 「おお」as "oo".
Since some are confused on the kanji:
大 - Big, large
Kun-yomi: おお-, おお.きい
This is the native Japanese reading used when the kanji is by itself such as in this sentence.
On-yomi: ダイ、 タイ
This is the Sino-Japanese reading used when it is combined with other Kanji (with some exceptions)
This is the reading used for 大学 - "daigaku" College, 大好き "daisuki" Very likeable, 大切 "taisetsu" Important
There are これ(kore)、それ(sore) and あれ(are). 'kore' means 'this', or the thing that is near your position (like when you introduce your bag to your friend). 'sore' means the thing that is near your interlocutor but not near you (like when you mention your friend's bag). 'are' means the thing that is far from both of you. (you mention the building that is far form you and your friend).
I see many native english speakers having trouble to figure out how does that これ それ あれ and この その あの things work. I ended up having to use the english-japanese plataform bc my native language, portuguese,does not have a japanese plataform apparently... But there is one cool thing about portuguese and that thing I mentioned above. In portuguese, we have the same sistem with more than one word for "this" and "that" It'd be like:
I guess it makes things a little bit easier if you're a portuguese speaker (:3 」∠) But tbh it is a little harder to learn in portuguese bc the second one needs to agree in gender and number with the word it references to as well (｀・ω・´) Like,
あの／ Aquele-Aqueles/ Aquela-Aquelas