How can I install the google play store app on my Samsung galaxy Ace?
There is a possibility your phone doesn't have any of the framework apps for google like maps, gmail, etc. If this is the case then the below will not work and you will have to flash the framework. The is already question here. If you have a Chinese edition you might be out of luck
Now if your phone is supposed to have gapps or had google maps and the other framwork apps then try this:
All you need to do is download the APK file Here and follow the steps
Place the APK file on your SD card
Install the APK by finding it on your phone where you saved it and clicking it. This can be done by using a file explorer. There should be one on your phone.
You may need to enable unknown sources by going to Settings ---> privacy and security and toggling the unknown sources setting