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
.afl Font Files Adobe Font Metrics File
.bdf Font Files Glyph Bitmap Distribution Format
.bkw Font Files FONTEDIT Mirror Image Font Files
.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
.otf Font Files OpenType Font
.suit Font Files Macintosh Font Suitcase
.tfm Font Files TeX Font Metric File
.tpf Font Files Transit NXT Pack Translation File
.ttc Font Files TrueType Font Collection
.ttf Font Files TrueType Font