I think you can tell the first letter of a word, but beyond that you'll have to let the layout program handle it.

Yeah, thats OT, right?

I think you are asking about "Initial Caps" the first letter of the paragraph made very large occupying the top telft corner of the paragraph spanning several lines. They are also called "Dropped Caps". Online they are created by some style code like CSS. But I do not know if there is an OT feature to substitute for them.
See http://desktoppub.about.com/od/glossary/g/Initial-Caps.htm

> Yeah, thats OT, right?

No, the layout program is not OpenType. OpenType is a font format. The software that does layout is something else.

Initial caps are often the same letters as others in the font, just larger. Setting such letters is primarily a feature of page layout (and CSS on the web), not an OpenType thing.

If there is a desire to make such a letter stylistically different, the Titling feature might be appropriate, or perhaps a Stylistic Set. However, there is no paragraph-level layout functionality in OpenType today. Setting the first letter of the paragraph differently would be done manually, or by a feature in the layout software (CSS, InDesign grep styles, whatever), and not at the level of the font.

There is nevertheless a Unicode character U+2029 paragraph separator. I wonder who asked for it and what it is used for. It is supported at least by the following fonts
http://www.fileformat.info/info/unicode/char/2029/fontsupport.htm