Complex sentence: Project Shield provides news, human rights, and election monitoring sites with protection from DDoS cyber-attacks by a system of caching (storing the data from the protected website to reduce load on the site).
Split into simpler sentences: Project Shield provides news, human rights, and election monitoring sites with protection from DDoS (Distributed Denial of Service). By a system of Caching (storing the data from the protected website to reduce load on the site).