You start with an uninhabited planet that you need to manipulate until it is able to sustain life. That means, starting with the landscape: building mountains, sculpting valleys, pushing up islands, creating oceans and seas, etc.
Then you need to establish the correct climate conditions, both in terms of temperature as well as humidity, that will allow the planet to thrive.
The next step is to plant trees that will feed the different creatures swarming around your planet. When it comes to animals, there is a wide variety: ants, tigers, dolphins, sharks, turtles, ducks, fish, and many, many more.
But be careful! If you raise your planet's temperature too much, it will become a desert... and if the humidity is too high, it will be constantly covered in fog. Take care of its ecosystem and make sure to maintain the different wildlife in proportion with one another, or else they will begin to disappear. These and many other options await you in your own virtual world.