eBook Files Extensions - What are ebook files and how do I open a ebook file?

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

File Type Category File Format
.epub eBook Files Open eBook File
.fb2 eBook Files FictionBook 2.0 File
.gpf eBook Files GRAVITY Ragnarok Online Patch File
.gpx eBook Files GPS Exchange File
.kml eBook Files Keyhole Markup Language File
.lit eBook Files eBook File
.lrf eBook Files Sony Portable Reader File
.mobi eBook Files Mobipocket eBook
.prc eBook Files Mobipocket eBook File
.pup eBook Files PlayStation 3 Update File
.zvr eBook Files SAFA Media Audio File