Why do humans have eyebrows?
Eyebrows function to protect the eyes from perspiration and provide shade.
Eyelids function to protect the eyes from foreign objects and sunlight.
Eyelashes function to protect the eyes from foreign objects, produce sebum (a lubriant that the eyelids) and acts as protection for the eyes from tears [1].

The above seems to be backed up by health how stuff works and the anatomy of the eye from emedicinehealth.
However, note that biologist dont have any concrete reasons for the eyebrow. This is just what many of them agree on I suppose. Here is another resource from sciencefocus.