Hello there,
You have not mentioned which entrance exam you are enquiring about. Generally you get the verification mail during the submission of the form. It contains your necessary credentials like your username or application number. For the important dates, you need to visit the official website of the body which is conducting this entrance exam. There you can find the last date of submission, the exam date, and other important informations. You should make sure that your application form is successfully submitted. If you think you have not received an important email (which you should have received), then you can call at their helpline number or send an email. The helpline number and the email id should be mentioned somewhere in the official website.
Hope this answer helps you.
Thank you!