When someone monetises something, they make money from it, like by selling ads or getting people to pay for it.
Monetising something is usually good because it means making money from it.
Examples:
She monetises her blog by showing ads.
The app monetises by charging for extra features.
He tries to monetise his videos by getting sponsors.
The company monetises its website by selling products.
The musician monetises his music by selling CDs and doing concerts.
The YouTuber monetises her channel by getting lots of views.