The customer related processes perspective is the perspective that shows the goals for the internal processes that have contact with the customer.
These goals will have some causal relation to the customer perspectives: When the marketing goals are met they should for example increase findability and trust on the customer level. Sales should help creating the right content for products, making them more relevant and usability friendly etc.

Also aftersales processes like payment and complaints handling are important as we want our customers to come back, become fans!
What will make you different from your competition is how you organize these proceesses, and how you define the indicators for these processes.
There are many more processes to consider as strategic for your website, but you should start with defining a small number of keyarea's and improve the rest later on.