Grammar Point:
The key difference is that 部 bù refers to an entire section or region, while 边 bian refers to a side or direction.

部 bù
部 bù is more formal and typically used to refer to regions in a directional sense, such as 东部 dōngbù (the East), 南部 nánbù (the South), 西部 xībù (the West), 北部 běibù (the North).
美國東部有很多大城市,像是紐約市和波士頓美国东部有很多大城市,像是纽约市和波士顿
The eastern part of the United States has many big cities, such as New York City and Boston.
台灣的南部天氣很熱台湾的南部天气很热
The weather in southern Taiwan is very hot.
台灣的北部有很多大公司台湾的北部有很多大公司
The northern part of Taiwan has many big companies.
明天東部地區會有大雨明天东部地区会有大雨
There will be heavy rain in the eastern region tomorrow.
中國的西部地區地形多樣,有沙漠和高原中国的西部地区地形多样,有沙漠和高原
The western region of China has diverse terrains, including deserts and plateaus.
边 bian
边 bian is more casual and often used in spoken language to refer to directions or locations, including 东边 dōngbian (the East), 南边 nánbian (the South), 西边 xībian (the West), 北边 běibian (the North), as well as 左边 zuǒbian (the left), and 右边 yòubian (the right) etc.
美國北邊有加拿大,南邊有墨西哥美国北边有加拿大,南边有墨西哥
To the north of the United States is Canada, and to the south is Mexico.
那棟樓在右邊那栋楼在右边
That building is on the right.
這家餐廳在公園的南邊,很容易找这家餐厅在公园的南边,很容易找
This restaurant is south of the park; it’s super easy to find!
左邊有一家咖啡廳,我們去那裡坐一下吧左边有一家咖啡厅,我们去那里坐一下吧
There’s a café on the left; let’s sit there for a bit.
你看,那個超市就在前邊你看,那个超市就在前边
Look, the supermarket is right in front!