A Microsoft file hosting and synchronization service.
Dear Neil,
Thanks for participating in the Microsoft Community. I'm an Independent Advisor and I'll help you.
When you create a Team in Microsoft Teams, it will create a SharePoint site, and a "General" channel, that channel will create a folder in the SharePoint principal library site called "Documents", so if you click in "Open in SharePoint", it will show those files in the Sharpoint library, in there, you will have the option to sync in your computer with the OneDrive client.
See more information in below links:
https://support.office.com/en-us/article/file-s...
https://docs.microsoft.com/en-us/microsoftteams...
https://support.office.com/en-us/article/sync-s...
Do not hesitate to ask if you need more information.
I hope it has been useful to you.
Regards,
Renzo.