An example of overall used as an adverb is the phrase "overall healthy," which means generally or mostly healthy.
An example of overall used as an adjective is in the phrase "the overall taste of the pizza," which means the general taste of the pizza.
An example of an overall is the denim trousers worn by a farmer.
The overall length of the house.
The overall costs of medical care.
My overall impression was favorable.
Enjoyed the performance overall.