medit uses autotools for the build. Quick build with default options:

tar xjf medit-x.x.x.tar.bz2
cd medit-x.x.x
./configure
make
make install

This will configure, build, and install medit to /usr/local.

If you checked out a copy of mercurial repository, then do the following to build:

./autogen.sh
./configure --enable-dev-mode
make
make install

You must have docbook, xsltproc, txt2tags to build medit from mercurial. Other
tools may be required and configure may not check for them, please report those
to the author.