To export a workflow to allow you to add this onto another platform, all you have to do is:
In the site that has the workflow you need to export:
Go to Work and down to Workflows
You will see a list of your workflows and on the righthand side is a button called Export. Select this and a new .xml tab will open, you need to save this.
Go into the site you need to add the workflow too and back into Workflows on the main menu.
Select Add new Workflow on the right of the screen.
Name the workflow as you would if you where creating one from new but where is states Import File add the saved .xml.
Then save. Depending on how big and how many formulas the workflow has depends on how log it takes to import. Once completed the workflow will open.