Xiaomi Mi4 phones that are imported from China don't come pre-installed with Google Play Store (only Xiaomi's own Mi Apps market is included). If you like Mi4's impressive hardware and are a little unsure about its software side, don't let the omission of Google Play Store deter you. Google Play Store is very easy to install and from it you can install whatever you want.
Here are the steps to install Google Play Store on Xiaomi Mi4:
2. Install the app by swiping from the top of your screen to open the notification drawer and tapping your recent download. You'll be asked if it's alright to install an app from Unknown Sources. Say yes.
3. Launch Google Installer and you'll see a list of Google apps you can install
4. Choose Google Play Store. It'll tell you that Google Play Store requires Google Service Framework to be installed along with other apps. In total there will be 4 apps to install. Just say OK.
5. Once all 4 are installed, you have a fully working Google Play Store! The first time you fire up Play Store you'll be asked to enter your Google credentials. For most people this means entering their Gmail username and password.