Answer:
A clinical diagnosis is the analysis made by a doctor when one goes to a hospital, which is simply based on symptoms or signs that the sick person has to estimate what disease they may have. A medical history of the patient or the signs that he presents are used instead of testing in a laboratory. This may result in an unspecified diagnosis. For example, if you go to the doctor and he sees that you have a cough, he can diagnose a flu, instead of doing a more thorough analysis.
As for the differential diagnosis, it is trying to identify a disease looking for similar characteristics in other diseases. This method is used to see first if we really have a more complex disease and thus be able to rule it out or analyze more options to treat it.
Taking the example of a cough, it would be to go to the doctor and tell us that we could have acute bronchitis, even if it is simply a flu.