What is grounding and how to do it?
You feel your connection to the planet. Go outside, take off your shoes, and sink your feet firmly into the soil. Feel the planet move so very slowly, feel the heartbeat. Match your mind to it. Grounding is the practice of keeping your planetary perspective, the long view, keeping yourself centered and balanced because you are not a mayfly, no matter how fast things SEEM to go. Choose steadiness
Some see grounding as a exchange of energy between your root chakra and the earth.
Breathe, do what @Anastasiya says. If you can’t actually put your feet in soil, that’s ok. You should try it sometimes. Regardless, it is important to be able to ground yourself anytime, so visualizing the Earth is fine in a pinch. (Like panicking in the bathroom before a presentation!)
Some grounding rituals will have you Imagine the flow of energy in your body. You can consider the energy to accumulate in your solar plexus chakras, then moving all the way down to the root, and into the ground.
Breathe in, the environment gives you energy, breathe out, send it to the Earth. (Or whatever you want really)
When you do it right, your legs might feel a little heavy as if you are being held a bit.
So try it anywhere. It takes a minute or two for a quick fix. For better results, do what @Anastasiya said.
Walk around your block with no destination other than to go around the block and come back. Do about a 20 minute long route at least. That simple. You’ll feel the earth move. You’ll notice shit you don’t usually notice and it will slow your racing mind down.