1. Web application is more into iis website
2. Each web application is associated with one application pool
3. When you create a new web application, you also create a new content database and define the authentication method used to connect to the database.
4. If you want you can add multiple content databases to the same web application.
5. As per Microsoft each content database size is 200 GB.
6. In each content database we can create 5000 site collections.