bobbyblank on "[Theme: Tortuga] Edit Child Theme Subfolders"

I can't figure out for the life of me how to edit a line of code in the domainname.com/wp-content/themes/tortuga/css/flexslider.css file and insert it into the child-theme. I see a ton of results for editing a child-theme's subfolder, but I'm not very tech savvy and immediately become lost in the jargon. Would someone mind giving me a step-by-step instruction on how to edit (call or whatever) a subfolder within a child theme? I made the appropriate edits and inserted the proper path in the child-themes folder, but I don't see any changes which were applied. Thanks!