This tool only sets the initial conditions for the liquid from a specific object. It does not continuously generate liquid as a Source from volume does in a container.
This tool can be used, for example, to simulate a drop of water dripping off an icicle.
It can also be used to instantly fill an object with liquid. For example, you can create a tube inside a glass, apply this tool, and then hide the tube.
Using Liquid from Object
Create a Liquid Container with a geometry object inside.
Select the geometry object to convert to a liquid.
The geometry object has to have volume to be a valid source for volume-based liquid. For example, this tool will not work on a curve.
Click the Liquid from Object tool on the Volume Fluids tab.
Select the container to set the initial conditions and press Enter to confirm your selection.
To change the display option of the simulation, alter the options on the Guides tab of the Fluid Object. For specific parameter help see the Fluid Object node help.