Their website explains that this "was proclaimed in 2011 by the UN General Assembly with the idea that friendship between peoples, countries, cultures and individuals can inspire peace efforts and build bridges between communities."
Here are some ideas for how you can contribute to international understanding.
WCC International Programs
Get involved with WCC International Programs by studying abroad, hosting an exchange student at home, or supporting related events.
Study International Relations
The WCC library's Credo Reference database has a great ebook to get you started.