This one's easy. An advert is an advertisement: just shorten advertisement, and you get advert. As a verb, to advert to something means to refer to it.
The noun advert (AD-vert) shows up mostly in England, where people use it interchangeably with advertisement, as in "Did you see that advert in the paper? If you buy two pairs of socks, you get a third pair free!" The verb advert (ad-VERT), on the other hand, means to "make reference to," like the way your mom might advert to your messy room and unfinished chores when you complain that you're bored.