Things you might want to put online include a list of your own papers (plus links to online versions, whether in postscript or HTML), descriptions of your work, personal biographies, or interactive demonstrations (see The Geometry Center for one example of what is possible.)
There are two different places users can put files to be served. I prefer the first.
~yourname/html. Any file in that directory is
directly on the Web. The equivalent URL is
http://www.santafe.edu/~yourname/.
/network/software/packages/www/export/users/yourname.
The URL for this directory is
http://www.santafe.edu/users/yourname/.
~ and ~/html in the first case),
and read permission on all files you want to serve.
One added feature of the server - if a URL ends in /, say
for example http://www.santafe.edu/~nelson/, then the server
first looks for a file named index.html. If that file does
not exist, then the server will build a default index by using the
directory listing.
Browse around the Web looking at what people do, what you like. Feel
free to look in ~nelson/html/ for examples of how to make
things work.