1.感叹句用来表达夸奖、感慨、惊讶、愤怒等。句末常用“啊、呢” 如：这里的风景真美啊！ 　　他还会做诗呢。 2.疑问句句末常用“呢” 如：我要喝啤酒，你呢？ 我的帽子呢？ 3.祈使句或问句句末用“吧” 如：帮帮我的的忙吧！ 　　 　　这道题不难吧？

if u wanna exlain ur mood,like suprise,u can use the word "啊"in the last of a sentence. if u wanna ask some things,u can add "呢" in the last of the sentence. if u wanna let someone do something,use the word "吧"。。。 these words' positions in sentences are the same,as usual they are in the last of sentences.... as Guang says,if u are a beginner,y'd better not focus on them,when u learn more,u can find these words not that hard to control,haha

Hi :) actually i have asked same question before and i got great answer. i think it will be your help too. here is the link of former question of mine, How do you describe those expressions 【啊、啦、唷、喔、哦】 http://www.italki.com/answers/question/28210.htm

i think you'd better to have some reading or communite with chinese peopel ,then you will get it easy . it is actually very easy ,coz they contain no meanings . just to help you to express your feeling better :)

1.啊 叹词，表示惊异或赞叹，常放句首。例如：这场雨真大啊！ 2.吧 助词，在句末表示商量，提议，请求，命令或表示同意，认可或疑问。 例如：1.咱们走吧！（表商量） 2.好吧。（表认可） 3.你不会不知道吧？（表疑问） 3.呢 助词，1.在疑问句尾表疑问。例如：我在哪儿见过你呢？ 2.在陈述句尾表确认事实。例如：这部电影挺好看的呢。