Its highly prefered to design your APIs before starting to develope them. With APIC's API designer you can do a lot than just designing API endpoints. To start either you can import an already exported APIC API projec or Swagger Spec or Open API spec or start from scratch.
To create a new API project click on the + icon and fill up the required fields like name, version etc and you are all set for designing your awesome API with APIC.
If you already have an exported API project or have an Open API specification (previously swagger specification) then importing that into your workspace is just a click away. Just click on the Import icon present beside your workspace and browse the exported file. APIC will import the project into your workspace.
Well, you can start some actual design.