1- Get out there with a bike
Of course, a purpose-built gravel bike is best suited for the discipline because of its geometry, gearing and tyre clearance. However, you can get started with any bike get on some light off road trails, and that are capable to take at least 30mm tire width. When I first started, I was borrowing a cyclocross bike from a friend.
2- Bring spares with you
Normally these are the basic things you normally bring with you on a long ride on the road, plus a few extras which you can carry all in your handlebar/frame bag:
-Multi tool with a chain tool
-Mini pump or CO2
-Fast repair foam spray
-Tubeless plug kit
-Patch kit
-Two spare tubes, even if you are using tubeless tire
-Electric tape
-Lights
-Extra food
-Money
-Spare base layer, jacket, neck warmer and gloves
3- Start by exploring
The best way to get started is exactly what I did at the beginning, explore around your area.
Don’t try to cover a certain distance; just get out for the adventure. If you have a friend that goes out with the gravel bike regularly ask them to show you some trails. You can also use Strava or Komoot to create and find some routes and upload them into your GPS bike computer.