Here are some examples of how "than a" is used in a sentence:
* Comparison: "He is taller than a giraffe." This compares the height of the person to the height of a giraffe.
* Quantity: "There are more than a dozen people at the party." This indicates a number greater than 12.
* Degree: "The movie was more exciting than a roller coaster ride." This compares the excitement of the movie to the excitement of a roller coaster ride.
To understand the meaning of "than a", you need to look at the entire sentence and consider the context.