Want to start creating theme but still failing

Hello guys!
I am new here and want to move my sites to Ghost. First of all I want to check how to create my own template to fit my needs. Right now im using Wordpress and Im totaly used to edit files the manual way.
In ghost cms I am not able to make any manual edits in templates. I’ve read some docs but still failed.
Can someone explain me the easiest and simplest way how to edit any of my template file to see this on my live website?