Installing graphics in DF is optional, but highly recommended for new players until they get used to the gameplay. There is one 32x and one 16x graphics pack I most recommend:
My favourite packs
Here we go, for my personal favourites:
My favourite tileset is Vettlingr 32x. You can download it in Graphics via Linux Dwarf Pack by just double clicking it, or you can install it manually here.
My favourite tileset for 16x is Wanderlust. You can download it in Graphics as well via Linux Dwarf pack by double clicking it, or you can install it manually here.
Installing other packs
To install other packs, first look around in your pack! They usually have great graphics packs. If you don't want to use the pack's graphics packs or you don't like them, this post can help you.