这两个基本用法是tell sb sth, say sth to sb.
tell sth to sbsth为某个事物say sth to sbsth为一句话或一个单词例如 tell the truth to your mom 告诉你妈妈真相say "i love you" to your wife对你的妻子说“我爱你”。
一楼的OK,一般都是说Tell sb something.
say sth to sbtell sb sth