after adding this pack to your launcher you must open its settings dialog menu (the little gear on the bottem left of the pack icon) and select the Downloaded forge latest 1.6.4 after that simple start the pack and it will be ready for use
Install Yanni Is a boss Pack
Step 1
Installing a modpack using the Technic Launcher is easy. If you don't already have the launcher downloaded, visit our download page to get the latest version.
Step 2
Type in the modpack name (Yanni Is a boss Pack) or paste the following url into the search box.
Step 3
Finally, click Install at the bottom right of the launcher after you select Yanni Is a boss Pack from the list on the left. The launcher will handle everything else!