Ok here is the Stupid Question Of The Day.
I am using as theme I did not create and I come across many instances where it is necessary to modify the code within the various php files. For adding code to the post itself I use a plugin called Post Layout and it works fine.
However, there are times when I am instructed to insert a code within a template other than the single-post template. In these cases anything I insert or modify is erased by the theme's upgrades (which are quite regular). The theme's author suggested I create a child theme to immunize myself from the upgrades.
Essentially what I am looking for is a plugin that will insert modifications to the theme that will survive an upgrade as the modifications will be retained within the plugin. Much like the Post Layout plugin.
So, what is a child theme and which is the easiest and simplest way to go? Child theme or some kind of 'code insert' plugin?
And where do I find this type of plugin if it exists? And where do I go to learn about child themes?