With many applications, there are multiple ways to download/install them. One way is through
apt-get and another is by downloading and untaring the .tar file. Note, that
apt-get has nothing to do with the .tar file.
Unable to locate package zopectl
Typically, that error indicates the package you are trying to install cannot be found in any of your defined repositories. Have you done a
sudo apt-get update? Run that command and then try again.
If you cannot get the
apt-get install to work, you should be able to install this application by untar-ing the .tar file (which you say you have already downloaded). In terminal, change to your home directory (
cd ~) and try this:
tar -xvf nameOfTarFile.tar
Note that if the file you downloaded is a tar.gz file, you'll need to set one more flag to get that to work:
tar -zxvf nameOfTarFile.tar