Advertisement -- this is a noun, sometimes shortened to "ad". (There are many advertisements on TV.) Advertising -- this can be used as a verb or a noun (and an adjective?). As a verb, it means to advertise. (Many English teaching companies were advertising during the Olympics.) As a noun, it means advertisements generally. (We don't plan to purchase any advertising this year.) Like many nouns, it can also be used as an adjective -- (the advertising department of a company) Hope that helps...

Advertising is the verb whilst advertisement is the noun. You can also say ' add'