[Koha] Trouble installing Koha

[Leila]

Hello all,
 I am trying to install koha (and use Linux) for the first time and am
   not very Linux savvy at all I   am afraid. I am having issues  with
   installing idzebra  but keep getting error messages regarding missing
   dependency libyaz3 which won't install because I keep getting this
   error message
    >> Depends: libgnutls13 (>=1.4.0-0) but it is not installable
   >> Depends: libicu36 but it is not installable
   Can anyone tell me what I am doing wrong and how to fix it?
   Thanks
   Leila