There are 2 ways to select topics. Whenever you select a topic, you can say yes to receiving alerts on your device.
One way to select a topic is to find the Topic given at the top of the article bolded either in Red or Blue, and click Add to myFT. You will notice that Topics are countries, companies, themes, or people .
The other way is to enter a keyword in the FT.com search box, and select one of the Topics in the results (again bolded in Red or Blue). Once on the Topic page of your choice, add it to MyFT.