I've been mediating for a while, since I was 26 (On and off throughout the years.) I am rubbish at it.
You sit quietly. You observe your thoughts. You observe your body. You observe your observations.
I've mostly used it as calming and checking in with myself, similar to journaling.
It's useful, but it shouldn't be used as a replacement for actual mental health services. It's not something employers can use instead of raising pay or reducing stress. You should always look at the causes of stress and if they can be changed, either personally or systematically.