To copy categories from another channel first navigate to the categories page for the export channel of choice. On the right hand side you can click on the button next to 'More actions'. When you click on the plus sign a menu will appear from which you can choose to copy categories. A pop-up will appear where you can select which webshop you want to copy the rules from and from which channel in that webshop. Click on 'From webshop' to select the webshop you would like to copy from and click on 'From channel' and select a channel from the drop-down list. Finally click 'copy here'.
Don't forget to click 'Save categories'!
After finishing your categorization you're ready to get started with the rules. How to manage your rules? Have a look here.