If you are using Ubuntu then the module BeatifulSoup is by default installed in it. You can find it using the command :
$ apt-cache search beautifulsoup
If you are using Python 3.x and still are not able to find it then install it using the following command :
$ sudo apt-get install python3-bs4
Once you download it then you can import it by following command
from bs4 import BeautifulSoup