Font Files Extensions - What are font files and how do I open a font file?

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

File Type Category File Format
.eot Font Files Embedded OpenType Font
.euf Font Files Private Character Editor File
.ffil Font Files Mac Font Suitcase
.fon Font Files Generic Font File
.suit Font Files Macintosh Font Suitcase
.tpf Font Files Transit NXT Pack Translation File
.ttc Font Files TrueType Font Collection
.ttf Font Files TrueType Font