When made public, your interests and favorite game are viewable to other players who look at your profile in the community chat room. It's a fun way to show other people who you are and what you like to do so. You may find out how to make this information public on private using this FAQ page.
To start off, these fields are all blank. If you'd like to set them for the first time or change them, click 'My Account' at the top-right corner of your screen and then select 'My Profile":
Once in your profile page, you'll see a section for My Games and My Interests. You will be able to use the edit buttons next to them in order to change your preferences:
After clicking 'Edit', you will be able to enter your new preference and two new buttons will appear. You will need to click 'Save' in order for your preferences to be saved.