"Young people in South Guangdong paint the future" refers to the younger generation in Guangdong. The meaning of this sentence is that young people in Guangdong contribute their own strength to the future development of Guangdong through their own efforts.
"Green and beautiful Guangdong" refers to the goal pursued by Guangdong Province in the construction of ecological civilization, that is, to build a green, beautiful and livable Guangdong.