Practise mixing colours and learn the basics in colour theory.
Materials:
Colour wheel free download: https://www.tarasage.com/art-materials
Paint kit which includes paint and brushes: https://amzn.to/49RtCa0 (Amazon)
If you do not need to buy a kit and already have paint, here are some brush options:
Mont Marte set https://amzn.to/3uXt4Rf (Amazon)
Meeden set https://amzn.to/49RtCa0 (Amazon -- these are the ones I'm using in the video that came in the one of the Meeden Acrylic paint kits)