Here's a list of the websites/apps currently blocked in China:
As you can see by the list, there are many popular sites/apps like Gmail, Facebook, Google, Twitter, and Instagram. If you see a website on the list, you should assume that BOTH the website AND the app are blocked in China. This means that you won't be able to access these websites/apps on your phone/tablet/computer during your entire time in China, starting as soon as the airplane lands and continuing until your airplane arrives at different country on the way home.
For some people, not having access to these websites/apps while in China isn't a big deal, but for others who prefer to be connected all the time and who like to post updates on social media and check email often, this could be a bigger issue. There are some ways for you to jump over "the Great Firewall of China", and luckily these companies all offer some sort of risk-free trial period, so you can download the app/program right before you leave, then cancel it when you come back from your trip, and it will be free for you (as long as you remember to cancel the service after your trip).
Make sure to setup your account and download the VPN app/program on your phone/tablet/laptop BEFORE you leave your home country and enter China. You will not be able to register and download a VPN service while you're already on the ground in China.
It's not guaranteed that the VPN will work every time for every app/website, but it's worth a shot to try it because most of the time it should work. Note that you can use these VPN apps/programs on your phones, tablets, and laptop computers. It's recommended that you setup accounts with more than one VPN service just in case you discover that one of them isn't able to be used.
Astrill (7-day risk free trial period)
Express VPN (30-day risk-free trial period)