How do I make CSS changes?

Hey guys,

I'm a beginner to Joomla and T3.

Have downloaded and installed the framework.

Would like to make changes to the CSS but everytime I make changes Compile LESS to CSS overrights my changes.

I have made my own theme folder. Do I copy LESS files into my theme folder to edit CSS or should I be creating a custom.css code.

Really confused what the correct workflow is.

Please help me