Dear madam and sir（国外比较女士优先）
My name is john,a graduate student from Jiangxi Solar Science and Technology Institute.(and并列连词相当于逗号的作用,一般不与,放在一起.还有学校一般都是地点+性质+school/college/university一类的)I writing to apply for the insurance company.（一个句子里不能有两个谓语动词,这里定冠词the可以指代就好了）At school,I major in community service.I master four languages（复数＋s）and passed Band Four in the College English Test.
During my four years' school life,I passed all the required courses with satisfactory marks.And Japanese is my major.
I would really appreciate it if you engaged me.