Market Orders Inquiry

I am having a huge brain fart when it comes to Mock Exam questions on Stop-Buy, Stop-Loss, Market/Limit Orders. Can anybody provide an example of when an investors would use such orders and if you could also include the difference between execution, validity and clearing instructions it would be greatly appreciated.

Thanks!

http://www.analystforum.com/forums/cfa-forums/cfa-level-i-forum/91326010