A short answer question uses a text box where you can type in a word(s) for an answer. Many questions of this type will ask you to fill in a blank or choose from a list of key words. Your submission has to match exactly with the answer on record, some of these questions do have more than one correct answer.
Things like spelling, leaving out spaces, or writing out the word number when the system expects a number will all result in a incorrect submission. However, these questions are not case sensitive, you do not have to worry about capitalization in your answer.