What is banner ad and how it works?

Banner ad is a form of advertising on the World Wide Web delivered by an ad server. This form of online advertising entails embedding an advertisement into a web page. It is intended to attract traffic to a website by linking to the website of the advertiser. These are image-based rather than text-based and are a popular form of website advertising. The purpose of banner advertising is to promote a brand and/or to get visitors from the host website to go to the advertiser’s website. They are simple and very important pieces of html and their presence on the web can make a big difference for internet-based companies and brands. 
Banner ads are intended to generate traffic to your website by linking to it and from there you try to seal the deal, whatever your deal is. Web banners work the same way regular print media advertising does: they inform, they notify about a new product, they grab your attention, increase brand awareness and so on.