Multiple wallets on Bitcoin Core Is this possible?

I've noticed that while viewing my 'Receiving Addresses' there is a button in the bottom left hand corner of the pop-up box which reads '+New'. If I click on this will it delete or overwrite my current receiving address?!

Thanks
A wallet is a collection of private keys that correspond to addresses you control; you can spend the coins that are credited to those addresses.

The "New" button creates a new private key (within the same wallet!) and shows you the address, so that you can ask someone else to send coins there.  You could reuse an address that someone else had already sent coins to, but this means that both senders would gain information about your financial activities (since all transactions are public).  Using a fresh address helps your privacy.

The "New" button doesn't affect existing private keys in any way.  Previous receiving addresses remain active and usable, and you can browse them in the address book.