This is often used with an object that has been converted to points. You can either store data on the points or instance geometry. Embed in Fluid is usually used for tracking fluid flow passively, by using marker particles.
This tool only works with volume based fluid.
Using Embed in Fluid
Create a geometry object and source within a container.
Click the Embed in Fluid tool on the Volume Fluids tab.
Select the object to embed in fluid and press Enter to confirm your selection.
Increase the Feedback Scale parameter on the Internal Forces tab of the Fluid Solver when using fluid to push a rigid body object.