Purpose: to discuss how to install and use the [tcllib] extension.

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Crude answer:  unpack the source distribution into a directory such as
  $MYDIR
so that there are files such as
  $MYDIR/tcllib/mime/mime.tcl

At the level of Tcl source, you don't use [tcllib]; you use packages from the tcllib distribution.  To use the [mime] package, for example, you might
  lappend auto_path $MYDIR/tcllib0.9
  package require mime
  # ... Now you can use any of the mime::* proc's.

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The safest thing to do though is to run the tcllib/configure [[make point of detailing which versions of tcllib have configure - versions since 2000 at least]] with the appropriate flags, then to run "make install" so that files end up in the location with the proper names, etc.

The appropriate flags do NOT have to be the same directories where
Tcl is installed; point at a $HOME directory for instance.

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'''WARNING!'''  Use Tcl8.2 or later with recent tcllib (certainly 0.8 and higher).  There are cases where in particular the code uses the new string functionality that appears in later versions of tcl to dramatically improve performance.  This results in locking tcllib currently into newer versions.

There have been discussions about people wanting/needing tcllib to
work on older versions of tcl working together to write some forward compatibility procs for tcllib, so that it can be used over a wider range of versions.  Alas, this work has not proceeded very quickly.