Hey Fatalitu,
To add a new AutoBuild template, place it in your .minecraft/wurst/autobuild
folder
Windows: Open your Windows Explorer and type %appdata%/.minecraft/wurst/autobuild
into the address bar.
(Alternatively, you can press Win+R and type in the same thing.)
Linux: Open your File Explorer and type ~/.minecraft/wurst/autobuild
into the address bar.
Mac: Open your Finder and type ~/Library/Application Support/minecraft/wurst/autobuild
into the address bar.
Hope this helps!