Practical steps.
CHECK FIRST
Many themes provide a child theme ready to download.
Use it rather than building one.
WHAT IT CONSISTS OF
A directory in your themes folder A style file with a header naming the parent A functions file enqueuing the parent's styles
WHERE TO PUT IT
Alongside the parent, in the themes directory.
ACTIVATING IT
Appearance, Themes. The child appears as a separate theme.
Activate it.
WHAT HAPPENS
Your site looks identical. The child inherits everything.
WHAT TO CHECK AFTER ACTIVATING
That styling is unchanged That menus and widgets are still assigned
Those sometimes need reassigning after any theme switch.
MODIFYING A TEMPLATE
Copy the file from the parent into the child, preserving the directory structure.
Edit the copy.
WHAT TO DOCUMENT
Which files you copied and what you changed.
In a year you will not remember.
