Package Files Extensions - What are package files and how do I open a package file?

What are package files and how do I open a package file?

File Type Category File Format
.cpk Package Files DTM Test Log File
.deb Package Files Debian Software Package
.epk Package Files Metin2 Game Data Package
.esp Package Files Fallout 3 Plugin File
.ipk Package Files Itsy Package
.lpk Package Files ArcGIS Layer Package
.package Package Files Electronic Arts Game Package File
.rpm Package Files Red Hat Package Manager File
.sims3pack Package Files The Sims 3 Package File
.unitypackage Package Files Unity Package File