Writing specifically for the purpose of selling your products or services is termed as Copywriting. When visitors visit your website, they expect to know as much as possible about your product or service in as little time as possible. That is the objective of Copywriting: you convert your website visitors to customers.
Few things that are needed to be taken care of in order to achieve that:
A proper description of your product or service that you provide.
The use of products and services provided by you to the customers.
Your Unique Selling Point(USP) that sets you apart from competitors.