How to duplicate/copy theme files

Hi Guys

I’m loving the simplicity of your product which is very easy to use and setup.

Having some difficulties accessing WP files as there is no directory on my computer that allows me to make changes to my WP files.
I am working to customize my webpages and came across this problem in me having to duplicate and rename some theme files.
The files I need can locate by me, no problem, but the question I would like to ask you is how can I access and duplicate them?

Thanks in advance for your reply!