TiM will only export the pages that have Export Tags applied within your Startwork Templates. The gray "Download" button allows you to download entire packets.
The orange "Payroll Company" Export Tag and the blue "Studio/Prod. Co." Export Tag are built in to TiM functionality, because productions typically need to send sets of pages to payroll and the studio. Many TiM Templates already have "Payroll Company" and "Studio/Prod. Co." Tags applied by default.
The purple, green, pink, and black Export Tags can be customized to define sets of pages that might need to be exported to other recipients besides the Payroll Company or Studio (for example, Unions or Health Officers). You can create custom Export Tags from "Tag Setup".