We recommend you set up a Google My Business profile for your business, this is a great way to boost your ranking on Google. In order to finish setting up your listing, Google will send you a letter in the mail to verify your business address. This letter contains a 5 digit PIN which you will need in order to finish setting up the listing. Until your listing is verified, your Google ranking will not receive any benefit of being listed, so it's really important to get this done as soon as you can.
The letter usually takes a few days, but can take up to two weeks to arrive. Once it's with you, all you need to do is follow the instructions on the card to verify your address. Make sure you do this as soon as you can, as Google PINs have limited validity, and will expire.
You're looking for a letter like the one below:
The front of the letter
Inside the letter: The 5 digit code in blue is all you need.
Once you have carried this out, Google will confirm with you that your business is verified and ready to receive reviews.
You may also receive another letter asking you to update your details using a special code:
Note that this is not the verification code that is required to verify your listing. If you want to use the code to change any details, you may do so, but be aware that this will not verify your listing and will not allow you to receive reviews.