In the Aeneid, Virgil uses symbolic images to create a tone. What is an example of fire, snakes, and storm images?
This is a great question. As you note, there are many images in Virgil's Aeneid. Let me name a few ways in which these images are used.
First, fire is a common imagery in the work. For example, in Aeneas' description of the burning of Troy, the fire there represents the destruction of his homeland, but it also shows Aeneas' courage as he rescues his family. A more subtle use of fire is the fire that is in Dido's heart and bones for her love for Aeneas. This can be seen as pointing to her eventual death as she throws herself on a fire in view of her unreciprocated love. Also keep in mind that the marriage torches go out, which shows that the love between Aeneas and Dido will not last.
Second, the snake imagery is one that is very interesting, because of the ambiguity of the symbol. For example, in book 5, at the grave of Anchises, the father of Aeneas, there is a snake. This could represent the favor that Aeneas has and the fact that his deceased father is looking out for him, or it can represent the fury of Dido, who cursed him at her death. If you recall, she stated that her shade will torment him. In the end, the reader is left to decide.
As for the storm imagery, storms are all over the place and this imagery usually represents the hardships that Aeneas will have to face to found a new land.