How to create a child theme?

It's really a piece of cake; let's take eprom for the example. Firstly, you must create a new folder (e.g. 'child-eprom').

Secondly, create a new file named 'style.css' and put it in your newly created folder. And then you should edit this file and enter some identification data:

Theme Name: Child Eprom
Desc: Eprom child theme
Author: your name here
Template: volumes
@import url("../eprom/style.css");
<span class="redactor-invisible-space">
/* Your styles below */</span>

And so, you've got yourself a child theme. Now you have to add CSS which modifies the theme below the import call.

When you want to change the functionality of a function in the 'functions.php' file you shouldn't modify it in the parent. Just create a new 'functions.php' file in your child theme and then add or modify the function. If you do like that then this function will be used instead of the default that exists in the parent theme.

More about Child Themes: