Become superuser and extract the gzipped tar file into an empty directory.
Make the installation directory /usr/local/stata14 and cd into it.
Type /wherever/extracted/files/are/install and follow the instructions.
For example, assuming you saved the archive in /home/you/Downloads,
% sudo -s
# cd /tmp/
# mkdir statafiles
# cd statafiles
# tar -zxf /home/you/Downloads/Stata14Linux64.tar.gz