The word in is as simple as the letter v. I am in the store. It is, "I am v the store". This is also the same symbol for the word at. Russian is goofy like that, if you think about it, it does actually make sense even in a literal translation; I am at the store, so this would also be the same as 'I am v the store". The pronunciation for this is, you guessed it - V or Ve or Va.
I am va the store - I am at the store - I am va the store - I am in the store - I am va the store
I am in the store