For some reason every time I open a type of package file to try and download, terminal just opens and the file does not install. What am I doing wrong?
Seems your file association is frelled up.
Right click on the .pkg / .mpkg file and select GET INFO and see what application is listed under the OPEN WITH section.
For me it looks like this:
I guess you have Terminal where I have Installer selected.
BUT then I have one more problem: I can't seem to find installer.app
Where is it located? In Utilities? for some reason its not there. Is there someplace I can download it?