Darko is an icon pack. It is not a stand alone application, you need a third party launcher to apply it.

***Note***
Please check the following videos on how to setup your phone with Nova and Niagara launchers:

Nova Launcher:
https://www.youtube.com/watch?v=B0npv8Z5sW0

Niagara Launcher:
https://www.youtube.com/watch?v=f3dvqiXTwC4&list=PLOvXK6kvTwvlCViyD1_BK3URZbPafQ5nN&index=4

Darko: A dark set with shadow for depth. Use it with any dark wallpaper for better depth effect.

What's included:

★ 4.144 HD icons (256x256)
★ 172 matching HD cloud wallpapers!
★ Launchers support: Action, Adw, AdwEX, Apex, Atom, Aviate, GO, Next,Nova, Smart, Solo...
★ Icon masking for un-themed icons
★ Dynamic calendar (For Nova Launcher)
★ Alternative icons to choose
★ Updates.