That boy in blue clothes is Jim.
那个男孩是谁?他是我的好朋友吉姆。 Who's that boy? He's my good friend, Jim.
there is a boy called Jim in his class
A boy named Jim.
Jim is the most serious-minded student in his class. Jim is the hardest studying student in his class. :)
Jim is an American boy，but he can speak English.