Google Plus notification on mobile phone is very much similar as on Facebook. The main advantage of mobile notifications is that when you don't have internet connection you will get the proper updates. Just you have to verify your mobile number with your Google Plus profile. Once you verified, you can control the notifications you want to get into your mobile phone, such as get notification if some one 'add to a circle', 'share a post with me directly', 'comments on a photo I tagged'.... and so many I can't explain here. Therefore, firstly you have to link and verify your mobile phone number with your Google plus profile page.