First of all, you'll need to download Microsoft's .NET Framework 4.5 if you haven't done so already. Here is a link:
https://www.microsoft.com/en-us/download/confirmation.aspx?id=30653
To download a title, follow these steps:
1. Load the program, and update your versionlists. (You can skip updating the versionlists if you know they are up to date or if you want the latest version.)
2. Search for/Click on the title you want to download.
3. Select a version from the list on the right side. (This step is optional if you want the latest version.)
4. Hit the download button.
To install the title that you've downloaded, you need to put
ALL the files that you downloaded (stored in the root directory of the program, in a subdirectory with the titleid, and optionally a version if you selected one... like this: "/program/titleid/version/") from this program (WITHOUT decrypting them) onto your SD Card in a folder called install. So, if your SD Card was mounted as the F: drive, then one example of the files should look like this: (F:\install\00000001.app)
If you want to decrypt the title for use with Loadiine or for your personal use (which is NOT needed if you want to install the update to the Wii U), then follow these additional steps:
1. Hit the decrypt button.
2. Navigate to folder which was just created (if you selected a specific version, then it would be "\rootdir\titleid\
version\", but if you got the latest version, then it would be "\rootdir\
titleid\")
3. Select the .bin of the Wii U Common key (which you have to obtain yourself)
Additionally, you can check the auto-decrypt checkbox in the settings to always decrypt downloaded titles. After the first time of use, the program remembers where your WiiU Common Key is stored, and uses that every time unless you move or delete the key.