Adwords is Google's advertising platform that lets advertisers market their product/service on the internet. It is a paid service that Google offers and is extremely effective if used properly. Depending upon the business your friend runs, Adwords can be used to market it by text, picture as well as video ads.
To explain it to you better, let me take an example. Suppose, I run an electronics shop selling mobile phones and other gadgets and have a shop in a local market. I also have a website that I use to get orders. However, the traffic to my website is limited and my store is only visited by people who are visiting the market.
Using Adwords, I can now promote and market my products on the internet in the form of ads. I can create a paid Adwords campaign and ask Google to display my ads featuring various gadgets at competing prices. Those ads are then displayed on the most visited websites and potential leads are then generated and forwarded to me/my website.
The results of a campaign like this may vary depending upon your product/service and the audience you are targeting. Please note, Google regularly runs promotions on Adwords and may offer you an additional credit over and above your budget if you are a new user.
I hope I was able to explain the concept to you. Please feel free to ask more questions.