This question is very difficult. Many Chinese can't clearly explain it. “做” is a verb. ”做~ “= （1）to do sth. （2）to make sth. (3) to be sb./sth. 做作业 = do homework 做练习 = do exercise 做晚饭 = make dinner 做准备 = make preparations 做贼 = be a thief 做猫 = be a cat “作” a verb / a preposition / can constitute a noun “作~”(verb)=（1）to compose sth. （2） to write sth. 作诗 = compose a poem 作曲 = compose music 作散文 = write prose “作”(preposition) = as “把……看作……”=think of sth as sth “作为一个学生”= as a student “作~”（noun） 作业 = homework 作文 = composition etc... sometimes it really comfused you. The easy way to use them is using a good input system. when you type a word or phrase , the system.will give you a prompt（not 100% true）

1.文字上有区别，这是三个完全不同的字 2.三个字的文法意义不同：作，一般与其它字组成名词，如作业，作为等 做，可以单独作动词，做什么什么事， 坐，则完全不同上面两个字，是表示一个动作，如坐下， 或表示一个状态，她坐在那里