Complex sentence: The very first mission of Yazda was advocating in the US and helped in support of US's mission to provide humanitarian food and water to around 60.000 Yazidis, who were stranded on Mountain Sinjar by ISIL the following week of August 3rd, 2014.
Split into simpler sentences: The very first mission of Yazda was advocating in the US during ISIL's attack on Sinjar. Yazda helped US's mission to provide humanitarian food and water to around 60.000 Yazidis who were stranded on Mountain Sinjar by ISIL in the following week of August 3rd, 2014.