it describe someone looks confident,open-minded,optimistic,just use the weather to describe people's performance and character,

to describe someone who is outgoing. 形容人阳光（的词语） I guess "the word" is omitted in the expression "形容人阳光“.

人很陽光，It describes that someon is cheerful and look on the brightness of life.

形容人阳光 means somebody is optimistic.