Thread: ClassiPress 3.3 ~ Child Theme Question

ClassiPress 3.3 ~ Child Theme Question

What exactly does Child Theme mean relating to the following?

I opened the navigational menu item I wanted to modify a selection (Read First) with a color. I see the CSS Classes and I gave it a name.

Then I was told to do the following but I do not know where I go to open a child theme.

Open your child theme style.css and place somewhere the color code that you like to use for that menu item. If you want the link to be red, write something like this:
#menu-header .my-menu-1 a {color: #FF0000;}

Where do I go to do this????
Thank you.