Doc. storage is a set of folders inside LedgerSync where your firm can keep each client's documents. To open it, go to the Tools menu at the top of the page and choose Doc. storage. The page that opens is called Document Storage.
The files are stored with Box.com through LedgerSync's own Box account, so you do not need a Box account of your own. This is separate from connecting your own Box account under Tools, Cloud Storage.
When you add a client to LedgerSync, a folder for that client is created automatically on the Document Storage page. Click a folder to open it, and click a file to download it.
Only users at your firm can open the Document Storage page. Your clients cannot open it, even when they are logged in to LedgerSync.
These folders only hold what people put in them. LedgerSync does not pull statements, transactions or check images into these folders, and it does not process the files stored here.