Installing the resource pack

You don't need to manually download the resource pack. It will automatically download once you login.
Some players experience trouble while downloading it, those players can get it here.
Be aware that your download will not update itself. You will have to redownload it every now and then to keep up with changes.

1. Download the resource pack for both worlds

You will need to download the resource pack for both the spirit- and the overworld.

2. Add them to your Minecraft resourcepack folder

Once downloaded, add both files to your Minecraft resourcepack folder. If you have trouble finding it, please follow the tutorial below. Otherwise skip and continue with step 3.

Now place both files in that folder without extracting them.

3. Open Minecraft and activate the resourcepacks

After putting the resource packs into your resourcepack folder you now need to activate both of them.
Start Minecraft and click on Options, then on Resource packs and move the downloaded resource packs to the right side of the screen by hovering over them and clicking them.
As you can see, both resource packs are on the right side of the screen now which means that they are activated and ready to use.

Tip: Disable the server resource pack while creating the server bookmark in order to not get annoyed with in game downloads.