Adding additional clients to shopify account

[BeefyT]

How do I add multiple clients to my Shopify account? Here's a website as an example of what I would like to do... The parent company is Bunker Branding https://www.bunkerbranding.com once you're at the site click on "Influencer" top left. From there it takes you to a page of "Influencers" that Bunker Branding provides order fulfillment services. What app or feature do I need for my shopify store to do what Bunker Branding does? I want to add multiple customers (Influencers) to my company.