Create CSS Stylesheet Folder file in WordPress Default 2012 Child Theme

Hi

WordPress version 4.2 has been released.

I am using WordPress Default Theme 2012. I have created a 2012 Child Theme for WordPress 2012. However, I do not know how to create a CSS Stylesheet folder or file for my 2012 Child Theme.

Can help to create a CSS Stylesheet folder or file for my WordPress 2012 Child Theme please?

Thanks and regards.

Benjamin