In order to store file uploads on dropbox, you will need to create an app from dropbox developer's website and enter those credentials in BeDrive settings page.
Open https://www.dropbox.com/developers/apps, click "Create app", then select "scoped access", "APP Folder" and enter any name for your app.
Open "Permissions" tab, enable all permissions in "Files and Folders" section and click "submit" at the bottom.
Go back to "Settings" tab and copy "App key" and "App secret" keys.
Open BeDrive "settings -> uploading" page, paste app key and secret you copied earlier.
Click "Get dropbox refresh token" button, then "Get access code" button. This will take you to authorization page on dropbox site. Authorize the app, copy access token, and then enter it into "Dropbox access code" field back on BeDrive site.