Viral content can be something unusual, something that seemed to happen of a sudden and is totally unexpected. A good joke or meme can also be viral content. Or, the contrary, something really sentimental and motivational. Anyway, it needs to be something with big impact, to make people aware. As for creating it... viral content usually comes to existence unintended, or intended but with a very good plan and script. So it would need a bit of online knowledge to see what got viral and try to emulate it or find smth better.