Hi mstouder
Depends what you are trying to do, if you want the whole package like the demo (which is easier if you are new to Joomla) then you need the quickstart package, if you just want the template then install Joomla and add the template package and extension package using the install from within Joomla.
For either you need to unpack the ja_sulfur_for_joomla_1. 5.x.v1.0.zip to be able to access the folders, template, extensions and the quickstart folder. Each contain their own zipped files.
If wanting the template you can work with the zipped files as described above. If wanting the quickstart you’ll need to unpack all the files in the quickstart folder and save in your root folder.
There is a detailed “how to’ it might be in the tutorials – if you can’t fnd it get back to me.