Just go to Glyphs, on the font presentation page.
Briefly, OpenType is a font format jointly developed by Adobe and Microsoft in the late 1990ʼs. It came into wider use only after 2000, when Adobe included support for advanced typographic features in their InDesign, PhotoShop, and Illustrator applications.
We offer fonts primarily in OpenType format. OpenType is the only cross-platform format, i.e. the same file will work on both Macintosh and Windows computers.
If you only work with Latin-based languages (e.g. English, French, Polish, Czech or Turkish) then our OpenType Std fonts will meet your needs. If you also require support of Vietnamese, Russian or Greek, then you’ll need OpenType Pro fonts.