hello I've been in the same situation as you. What I did was to look into the controller and find the private function installBlocks ($ pkg). Here you can find the name that must install the package, because some times you have to change it.
Otherwise, I think you have to put the contents of the package file inside the package folder.

What controller? How do I look at it?

You should use the /packages directory that is in the root folder.
Content under the /concrete/ directory has to do with the core functionality of the CMS. All code changes you make can be done inside the /applications directory. But for installing packages, they go in the root /packages/ directory. IF you are installing standalone items, such as a block, or theme, that is NOT in a package, you manually put those files into the /application/blocks directory or /application/themes directory. But one of the points of making a package is so that end users can put the file into the /packages directory and the package put everything where it goes for you.