教师 is a career or occupation while 老师 is more like a title or an appellation. 教师 is definetly refers to a person who take teaching as an occupation. 老师 on the other hand could be used in a lot of circumstance, you can call a teacher, a professor, a writter, a journalist,a barber or anyone is professional 老师. Here it does not mean teacher anymore, instead, it only shows the respect.

Hi Oscar, you have good reasons to feel confused for typing "那人" （or 哪人 for that matter）. This is one of the rare cases when popular typing systems don't follow standard rules in PINYIN. Yes, technically, the PINYIN for 哪儿 is "nar", but for the sake of convenience or whatever, we type "na er", as they map more obviously onto the two characters.

For the first one, you could say"我该把脏衣服放哪儿?" or just "脏衣服放哪儿?". The second one is correct. The word "老师" is more common in our daily conversation, like"这是李老师"，"我是小学老师"，"你的老师叫什么名字?". While "教师" is more formal. For example, the Teacher Certification is called "教师资格证", and the Teaching Skills Competition is "教师教学技能大赛".

Thank you so much! 谢谢!

The correct sentence is 我该把脏衣服放哪？（where should I put the dirty clothes?)