Once you've un-tarred the files as explained below, help is available in the README file in the plt/src sub-directory.
You will need root access for this. Do the following:
% cd
% tar -xzvf plt.src.x.tar.gz
% cd plt/src
% ./configure
% make
% make install
% cd ..
% ./install
Now you can run DrScheme by typing:
% ./bin/drscheme
To make a symbolic link into your /usr/bin directory so that you can type drscheme from anywhere if /usr/bin is in your path:
% ln -s ./bin/drscheme /usr/bin