For understanding this first you need to know the structure of a Request
Where URL - Is the resources you want to access to like example- http://example.com
Method- what you want the server to do, like do you want the server to POST, PUT, GET or DELETE
Header- Contains the meta-data of your request
Body- Contains the information which is required to process the request.
Suppose if you want to insert a data into the database, you have to first get the data from the user (Which is present in the body of your HTTP request) and then insert it into your database through your application.
So what exactly your express .get() method does is that it is used to get the raw data. But if you want only the data which is present in the body of your request then you have to parse using body-parser.
const bodyParser = require('body-parser');
// support parsing of application/json type post data
app.use(bodyParser.json());
//support parsing of application/x-www-form-urlencoded post data
app.use(bodyParser.urlencoded({ extended: true }));