Start with this playlist. Watch the first 5 short videos and the first long one.

https://youtu.be/IoPUOJn6gQA?list=PL...XKU_1z5sHaw a

And this PDF. https://www.vipassanaforum.net/meditation/Shamatha.pdf

It's nothing fancy, just the basics of mindfulness meditation but that's without a doubt the best place to start.

If you want some info on the science behind mindfulness this is an excellent video.

https://youtu.be/5TeWvf-nfpA?list=PL...ydVp1WpVnPNokg