To install Helpful, go to your WordPress admin and click on Plugins. There you click now on add new. Here you search for Helpful, the first entry should already be Helpful. When you have found Helpful, click on Install now. Once you have installed Helpful, click Activate.
If this doesn’t work for some reason, you can also install Helpful manually. To do this, first download the file here. Once you have done this, click on Plugins again in your WordPress admin and then on Add.
Here you can now click on Upload Plugin above. There you select the downloaded ZIP file and upload it. Once you have done this, you can activate Helpful.