Restore Web Application By Using Content Database Backup

Below are the steps on how to restore a SharePoint web application by using the content database backup. (e.g. Testing2 is the name of content database backup)

1. Go to the SharePoint central administration and create new web application with the same name & database name that you will restore.
2. In Application Management >> Content databases, select your newly created web application and then delete the newly created content db (remove content database)
3. In Sql Server, restore your content database backup. If there's an error saying that it's currently in use, just wait for 3 to 5 mins and then try again.
4. In Application Management >> Content databases, add a content database. Set the database name equal to the restored content db in step 3. (for this case, it's Testing2)