You can use it for anything you want it to. Ummmm.
The Internet. Watch movies. Listen to music. Shove it in poor people's face to show how much richer than them you are. idk.
You don't really need a security app unless you lack common sense or like taking risks with downloading shady apps from shady sources.
I personally am an iTard using an iPhone, but these articles will probably point you in the right direction about security.
http://www.digitaltrends.com/mobile/...curity-basics/
http://www.digitaltrends.com/mobile/...security-apps/