I want to learn how to complete the following program. One entity (entity 1) is moving along X axis. On it, there is another entity (entity 2) that is moving on the first entity. Is there any function to handle this?

To note that the second entity is not always on the first entity, so I don't want to use bones ( If I am wrong please correct me - I am a beginner)

Here is a picture to better depict the idea.