The Check Out tool will allow you to download a copy of a customer folder from the NRCS servers to your computer in an editable mode, while disabling edition for other users. You won't be able to check out a folder if another user is currently checking it out. If the folder is currently checked out, it will show up in the "Folders in NRCS server" left panel (see Customer Folder Search Overview) colored pink; otherwise it will show up colored green.
Whenever you check in a folder, you'll see a box similar to the one below, informing you of the different check out stages. Wait until this process is completed.
You'll notice the folder you downloaded now appears again on the right panel, which contains the customer folders that are available locally (in your computer).
It's colored green, with a writing pencil icon, meaning that you can modify it.