According to the installation instructions on their website (http://www.sweethome3d.com/userGuide.jsp#installation
), you just need to extract the files from the archive you downloaded and run the executable you find in the directory that is created from the extraction. You can extract the files from the archive with
tar xvf filename
is the name of the archive (and I'm assuming that it's in the current directory) and it should create a directory with the files in it. From the output during the extraction, it should be obvious what that directory is called. You can then change to that directory and run the executable. The options used for tar are
x - extract
v - verbose (i.e. it tells you what it's doing)
f - to specify the filename
and more info can be found by reading the man page.
Edit: you might also not want that directory to live in your home directory. So, one place you could move it to is /opt, with
sudo mv directory
where again, directory
is the obvious. Then, you'll probably want to make a symbolic link to the executable in /usr/bin or somewhere else in your PATH. Ask if you need/want help with this.