do note that lnp isnt updated to the latest version because of issues getting memory layouts for the 64bit version of df, which is new.
lnp has some great utilities that will help you when learning the game, but if your intrested in all the !!FUN!! you will have from playing without utilities heres how to install tilesets (thats what we call texture packs)
step 1: find the tileset you want, the wiki has a tileset repository. tilesets are just a single image. i personally reccomend taffer if your looking for something simmilar to default, but square. and obsidian for something more fancy.
then head to where ever you put df and go to (i think) data, art, tilesets. im not at my computer atm so i cant check.
put the tileset there and then look for the init folder, there should be 2 diffrent init files, init and d_init. in one of them there should be 4 lines where it says ”"curses_800x600" replace all the instances of that with whatever the file name of your tileset is called.
note that any worlds already generated will need to have their raws replaced to use the new tileset.
also, in case nobody has given you a proper welcome:
welcome to the bay 12 dwarf fortress forums, please leave your sanity at the door and throw your morals down that bottomless pit over there.
around here, throwing a child into a pit of pulsating spikes surrounded by trained war dogs constantly clawing at them for the next 8 years of their life, murdering members of nobility and passing their death off as an unfortunate accident, and torturing elves for sport is all considered common practice and good fun.
this is a safe place to let your inner psychopath that wants to commit complete global genocide upon every living creature in the most creative and horrendous ways possible roam free