First of all, what’s a modifier? Basically it’s a word or phrase that describes what you’re talking about (the grown-up/technical definition: it’s an adverb, adjective, phrase, or clause that acts as a modifier (but I don’t like it when you use the word you’re defining in the definition)).
A misplaced modifier is when you put the word in the wrong spot and thus describe the wrong thing:
Wrong: The students were told their test would only cover cosmetology by their teacher.
Right: The students were told by their teacher that their test would only cover cosmetology.
Wrong: (This one courtesy of Jan Venolia): He told her that he wanted to marry her frequently.
Right: He frequently told her that he wanted to marry her.
