This guide will assist you in understanding how to upload multiple documents at one time to a single document library.
Login to your SharePoint site and click on the document library you wish to upload files to. Once you click on the document library, up in the ribbon, click on the Files tab
A new window will pop up. You need to click the link that says "Upload files using Windows Explorer instead"
Once you click the link, a windows explorer window will open up. You can now open up another windows using windows explorer and navigate to your file share and drag and drop your files/folders to the other windows explorer window and it will upload to sharepoint.
**In order to get the windows explorer to work correctly, the SharePoint site must be in the trusted zone of the internet browser.
**This only works with Internet Explorer (32bit) and only on Windows. This does not work like this on a mac.
**The WebClient service must be running on the windows machine (check services.msc)
**If all of above is in place, and you still get an error, sometimes you just have to refresh the internet explorer on the SharePoint site and try again. It usually works the second time.