One of the main differences between LaTeX2e and LaTeX 2.09 is that LaTeX2e can deal with fonts in arbitrary encodings. (A font encoding is the sequence of characters in the font--for example a Cyrillic font would have a different encoding from a Greek font.)
The two major font encodings that are used for Latin languages such
as English or German are OT1 (Donald Knuth's 7-bit encoding, which
has been used during most of TeX's lifetime) and T1 (the new
8-bit `Cork' encoding).
LaTeX 2.09 only supported the OT1 encoding, whereas LaTeX2e has
support for both OT1 and T1 built-in. The next section will
cover the new commands which are available if you have T1-encoded
fonts. This section describes new commands which are available in
all encodings.
Most of these commands provide characters which were available in
LaTeX 2.09 already. For example \textemdash gives an `em dash',
which was available in LaTeX 2.09 by typing ---. However, some
fonts (for example a Greek font) may not have the --- ligature,
but you will still be able to access an em dash by typing
\textemdash.
\r{<text>}
This command gives a `ring' accent, for example `o' can be typed
\r{o}.
\SS
This command produces a German `SS', that is a capital `ß'. This letter can hyphenate differently from `SS', so is needed for entering all-caps German.
\textcircled{<text>}
This command is used to build `circled characters' such as
\copyright. For example \textcircled{a} produces
.
\textcompwordmark
This command is used to separate letters which would normally
ligature. For example `fi' is produced with
f\textcompwordmark i. Note that the `f' and `i' have not
ligatured to produce `fi'. This is rarely useful in English
(`shelfful' is a rare example of where it might be
used) but is used in languages such as German.
\textvisiblespace
This command produces a `visible space' character
` 
'. This is sometimes used in computer listings,
for example `type hello world'.
\textemdash
\textendash
\textexclamdown
\textquestiondown
\textquotedblleft
\textquotedblright
\textquoteleft
\textquoteright
These commands produce characters which would otherwise be accessed via ligatures:
The reason for making these characters directly accessible is so that they will work in encodings which do not have these characters.
\textbullet
\textperiodcentered
These commands allow access to characters which were previously only available in math mode:
\textbackslash
\textbar
\textless
\textgreater
These commands allow access to ASCII characters which were only available in verbatim or math mode:
\textasciicircum
\textasciitilde
These commands allow access to ASCII characters which were previously only available in verbatim:
\textregistered
\texttrademark
These commands provide the `registered trademark' (R) and `trademark' (TM) symbols.