There's no getting around it. Virgil's Aeneid is a very tricky book. On the most basic level, it's going to throw a lot of weird and sometimes obscure cultural material at you that you might not be familiar with. These include mythological characters, place-names, and historical references. To help you with these, keep an eye out for an edition with at least one of the following: a good introduction, footnotes, and a glossary of names. These will be the Sibyl to guide you through the underworld.
Beyond that, there is the fundamental problem of Virgil's highly nuanced portrayal of his hero, which to this day puts food on the table of scholars who argue about whether Virgil thinks Aeneas is a good guy or not, and, if so, to what extent. (Once again, a good introduction, especially to one of the more recent translations, like the one by Stanley Lombardo, will help you out here.)
What really makes things difficult, though, is the incredible care Virgil put into investing every line of his poem with the maximum amount of meaning (take a look at our "In a Nutshell" section for a closer look at the poet's working methods). This usually means a complex texture of allusions to Homer and a variety of other ancient sources – many of which you've never heard of before. (Think of the elaborate learning of someone like James Joyce and then take him back 2000 years.)
The point of all these warnings isn't to scare you away from Virgil's poem – far from it. We just want to let you know that, if you do have trouble with it (and you will), you're in extremely good company. That said, there are countless passages in the Aeneid that are extremely exciting, moving, or just plain beautiful, and you won't need anybody to tell you which ones these are. These are the reason why Virgil's Aeneid was a basic school text-book throughout the ancient world, and why it has had such an incredible influence on nearly every European art form ever since. The poem is there waiting for you; all it takes is the gumption to dive in!