There are two answers to this question.
The first place to visit to learn how to use the software is not
online, but instead the Users Guide that is part of the download.
There are a number of examples of analyses to perform.
The other source of tutorial information is online material I will
be developing over the next three months. We will be creating a new
section of the
http://distancesampling.org website, devoted to not
just one, but a series of vignettes, or tutorials describing the
performance of a series of tasks with Distance; such as specifying
detection functions, interpreting goodness-of-fit statistics, model
selection tools, special topics such as point transects; and many
other things. These will be posted onto the
distancesampling.org
website and I will post notices to this list as they become
available.
There is also a set of vignettes describing use of distance sampling
software associated with the R software at the bottom of
http://distancesampling.org/R/index.html This list will also be
growing with time.