have sth to do---有某事要做。 例如:I have a lot of work to finish.---我有很多工作要完成。
have sth done ---让别人把某事做了。(可以按have sth done by sb.理解) 一般当只强调某事被做,而不强调被谁做的时候用这个短语。 例如: I had my hair cut yesterday.--昨天我剪头发了。(隐含让别人比如理发师剪的)(这里cut是过去分词形式,cut的原型,过去式,过去分词都是cut。)
have sth do---正常是have sb do 等同于let /make sb do ,让某人做某事。 例如:The teacher has his students make a sentence.---老师让他的学生造一个句子。