You can always save your progress when going through the Collection page by clicking ‘Save as Draft’
The next prompt involves choosing which type of artwork you'd like to upload to your collection:
Upload your complete collection: this option is suitable if you have your full artwork ready to go
Build your collection using layers: Fair.xyz supports generative collections which are created through programmatic combination of layers/traits. If you'd like to create a generative collection by uploading your layers/traits, this is your best option!