Your software
My Mautic version is: 3.2.1
My PHP version is: 7
My Database type and version is: 5 +

Your problem
My problem is:
while creating my own email when i am selecting anything from insert tokan that is not coming like
if i have selected {contactfield=firstname} than after preview it is showing [First Name].
please help if any one faced the same problem.

Hello there!
[First Name] will appear in Preview and in Example email, because otherwise your would always have blank as there is no contact identified. Do not worry about the “real” emails data, it will show up.

Thank you for replying. I am getting same error [First Name] if i m doing {contactfield=firstname} in Landing page. how can i resolve that. can you please tell me the steps

To see the proper name you need to enter the page as identified contact, most easily by proxy link sent in email (the long one with token), or using a browser where a contact was identified and identification data is still held.
Make a segment email, include {pagelink=x} in the body and send to your test segment.

Also important to make sure you are viewing from a browser that you are not logged into mautic