QUE
The relative pronoun que is used in sentences in which the antecedent is a person or a thing. The sentence introduced by the relative pronoun que helps to clarify or specify the idea expressed on the main sentence.El niño tiene problemas de salud.
The kid has health issues.
El niño que tiene sobrepeso tiene problemas de salud.
The kid who is overweight has health issues.
The sentence is more specific with the relative clause introduced by the relative pronoun because now we know what specific kid we are talking about.