I wonder what influencer marketing is.
It's a type of marketing that's focused on individuals. You see it in social media. 
Who well know infuencer should I know?
The Kardashians might be an example. Their tastes influence certain potential buyers.
What products do they promote?
Different diet, fashion, and cosmetics. Influencers sometimes basically give testimonials to how much they like a product, and that makes others want to buy it.