Debugger calculates the address for you and shows it after @, in your case it is $B0B8.
This addressing mode is called "post-indexed indirect". Indirect is when your final address is stored in 2 adjacent addresses in little-endian format. Indexed is adding value from an index register X or Y to the address. Post is adding index register after calculating indirect address.
LDA ($2B),Y = low byte at $002B, high byte at $002C. For example $002B = AB, $002C = 89. 89 & AB = $89AB. Then you add Y to this address to get $89AB-$8AAA range you can work with, which is 256 addresses in total. If Y = 05, then LDA ($2B),Y = $89AB + 05 = $89B0.