Follow below steps to import masters from Busy to Book Keeper Windows:
1. Open Busy on your Desktop
2. Go to Administration > Data Export/Import > Data Export/Import (XML) > Export Data > Masters
3. A new window will open, choose Account or Item or both and click Export, save it to Desktop
4. Open Book Keeper Windows > Tools > Import Data From Busy > Select that file which was saved in step-3 and click Start Import.
Here's video tutorial for your reference: https://youtu.be/5m_bUCd4pNs