A referential approach in semantics is when language is used to refer to something in the world. For example, if you say “I am in Florida” the speaker (you) is the referent of the word I and the referent of the word Florida is the state of Florida.
Here you can see that there are two different types of reference: constant and variable reference. In the above example, I refers to the person who is speaking. This is the referent. If I (Josh) said the sentence, the word I would be referring to the human Josh. If you said the sentence (feel free to say it out loud right this moment), then the word I would refer to the current reader of this website.
A similar example is the term president of the United States of America. If you say this at the time of this writing (2019) the term would refer to Donald Trump. The term the president of the United States of America would refer to Barack Obama if the phrase was uttered in 2010. This is variable reference.
The word, Florida, however, has constant reference. The word Florida will always refer to the state of Florida.
Some words do not have something to point to in the real world; they don’t have a referent. For example, the word unicorn doesn’t have a referent as the word cannot point to something that doesn’t exist.