Scraping information from websites

I am trying to scrape information from a website and store it in my apps SQLite database. I have seen it done before in some apps, whereby the user is able to navigate to a website and from there they can press a button and specific information will be scrapped form the website and then saved to the database.

My question is, how is this achieved or where is the best place to start with scrapping from a website and storing the information?