Thats a veeerry huge question. That's like saying "what does beer taste like" or wine or cheese.
The only ingredient that meads have in common is honey. Other than that, it can be anything. There are traditionals, melomels, metheglins, acerglyns, pyments, cysers, braggots, bochets... the list goes on. Mead is a huge and fascinating field to jump in to.
I highly suggest doing the JAOM first. It's cheap, nearly foolproof, and pretty damn tasty. I keep a batch of it around for mead-virgins because it's sweet and drinkable and it's a good "gateway mead."
Good luck and happy mazing!