Can someone help me with descriptions?

but I guess you want to make unique name for landmarks? this however need new building to be added to demesne but it is unique to what kind of demesne it will show up.
for example you want to add red keep in Castle red keep in Kings landing.

you need to make unique building for that barony by making new building in the building script in common>building

you can either made new script or modify existing by adding that building you want to make.

for example:

ca_con_wall_7 = { # The Red Keep name of this building (this line with # will be ignored by the game serve as reminder for you for what is this all about)
potential = {
OR = {
holder_scope = {
AND = {
#can be or of "one of this must be true"
#can be and of "all of this must be true"
OR = {
culture = high_valyrian # only high valyrian are allowed to build this
trait = ambitious # if you make trait as prerequisite or you can change it to barony 
title = b_kingslanding # need to be exact as the barony name in game file or county if it is county specific building.
}

desc = ca_con_wall_7_desc # the description of this building in localisation
gold_cost = 5000 # cost of the gold this is base cost can be vary do various changes and modifiers in game.
build_time = 3600 # 10 years as it is represent the game days, this also base time to build in vanilla this will be reduced when you have high level construction or have char modifier diligent on time.
fort_level = 14.50 # building stats so this as example as fort level, garrison, number of troops it's provide, tax income, etc you name it from that structure, this also represent base amount/level.
garrison_size = 1.00 # 1.00 will be 100% bonus to garrison this is multiplier in amount
horse_archers = 1500 # this will be exact amount of troops exactly 1500 horse archer will be added into demesne troops pool, you cannot add multiple special troops such as elephant.
knights = 1000 # Knights is common troops it can be put together with heavy infantry, archer, pikeman, light cavalry or light infantry.
tax_income = 5 # this will be exact amount will be added 5 tax PER YEAR.
ai_creation_factor = 25 # chance AI will do/build this building if they have power to fund it meaning lower factor compared to other building less AI will choose and ignore it.

extra_tech_building_start = 0.0 << AGOT not using any tech so can be ignored for now
}
then you need to made changes in localisation as above or else the building will not have any names and appear as ca_con_wall_7 and have description as ca_con_wall_7_desc, if your building only have 1 single word it can be put here to replace ca_co_wall_7 for example as arbor but you cannot do capital letter and have unique character in it.

some other command to be inputted above :
upgrades_from = xxxxx #  represent what structure this building from as this structure will replace previous structure before it.
prerequisites = { xxxx } # represent what should be build in this demesne before this building is unlocked, for example you need castle town before building Red keep.
trigger = { xxxx } # represent trigger to unlock this building for example tech 

and many others it's just too much to put it all here.