To talk about things being in places, use the word 在 (zài). This is actually a verb, so you don’t need to use any other words to talk about something being somewhere.

The structure is:

[something] 在 [place]
Have a look at some example:

我在这里。
Wǒ zài zhèlǐ.
I am here.
你在那里。
Nǐ zài nàlǐ.
You are there.
上海在中国。
Shànghǎi zài Zhōngguó.
Shanghai is in China.
猫在沙发上。
Māo zài shāfā shàng.
The cat is on the sofa.
Notice how English uses the verb “to be” where Chinese uses 在. English also uses prepositions - “to be in” - whereas Chinese often just uses 在.