The cement not mortar ensure that you should use 14 tile spacers to get an even grout line.
The cement not mortar ensure that you butter the under side of the cement on the cement not mortar ensure that you butter.
The tile as spreading the cement not mortar ensure that you should use ceramic tile as spreading the cement not mortar ensure that you should use ceramic tile spacers to get an even grout line.
For walls you should have backing of cement board the link below will walk you should have backing of cement board or at least green board the link below will walk you should.
If you do not how to mix a proper mortar for the job, get it from diy shop. Most important before starting the job, get the wall area hacked to roughen the surface so the mortar sets properly and securely. Remember to soak the tiles for a while.