Explaining how to generate gaseous fluid dynamics is beyond the scope of this manual, but we can get you started. If you want to learn more about fluid dynamics, the Blender manual is a good place to start.
To render a Smoke volume:
Create a sphere (used as an emitter) for the flow by pressing Shift+A and selecting a sphere. Then define it as a smoke fluid by going to the Physic Properties tab and clicking the Fluid button. Enter these values:
Figure 1: Creating a sphere emitter
Create a cube for the smoke's domain. The cube needs to encompass the sphere emitter or no smoke will be created in the domain. Select the cube, then go to the Physic Properties tab and and clicking the Fluid button. Enter these values:
Figure 2: Gas Domain for smoke
Create a MaterialThe representation of the surface or volume properties of an object. for the cube.
Figure 3: Creating a new Material
With the cube still selected, switch to the Shader Editor view.
Figure 4: Selecting the Shader Editor
OctaneRender® applies a Universal material, but since you are using a Volume, replace the Universal material with an OctaneRender® Volume medium and connect it to the Volume input pin.
Figure 5: Adding a Volume medium
Figure 6: Volume medium connected to Volume input pin