An advert is an announcement in a public medium or social media promoting a product or service or publicizing an activity.
The main function of an advert is to bring in new customers or re-establish contact with existing ones.
Advertisements target specific audience in specific ways. There is a target audience the advertisers are aiming for.
For example, a company that is advertising hearing aids wouldn't target younger people, its target audience would be older people with hearing problems.
the first paragraph provides insight as to just what a ukelele is, the second contibutes the components, and the third informs about the history of the instrument.