To use merge tags in emails created in HTML you can find it under Personalize dropdown.
If the email is created in Template Designer you can find Merge tags under Recipient Details dropdown.
The list below outlines all of the tags available to you.
Merge Tags for Headers
%viewemail%
View On Site Link -allows your subscribers to view your email message in their browser.
%unsubscribe%
Unsubscribe Link -allows your subscribers to opt out from your mailing list.
%forward%
Forward Link - allows your subscribers to forward email to friends.
%nevermail%
Nevermail Link - allows your subscribers, who do not wish to participate in any marketing emails, to be removed from anyone that uses Emercury.
%cur_date%
Current Date - allows you to insert in email date of campaign sending.
Social and sharing merge tags
%button_f%
Facebook / Like Button - it adds a facebook like button that allows your subscribers to like your campaingn in facebook.
%button_t%
Twitter /Send A Tweet - it adds a Tweet button to your campaign that allows your subscribers to share your campaign.
Merge Tags for Confirmation Page and Welcome Email
%user_field_9%
Optin Date - this will show the date the subscriber chose to optin to the website or purchased a product/service on your website.
%user_field_8%
Optin IP Address - this will show the IP address of the subscribers computer. This is collected at time of signup on the Optin Website.
%user_field_7%
Optin Website - this will show the website address that the subscriber opted to receive information from.
Merge Tags for Personalization
%email% - this inserts your subscriber's email address
%user_field_1% - this is used for First Name
%user_field_2% - this is used for Last Name
%user_field_3% - this is used for Gender
%user_field_4% - this is used for DOB (Date of Birth)
%user_field_5% - this is used for City
%user_field_6% - this is used for ZIP
Merge Tags for Tracking
These are commonly used inside URLs for tracking
%list_id%
List ID - this will insert unique identifier of the list, that you are sending to.
%report_id%
Report ID - this will insert unique identifier of the report, that you are sending to.
%campaign_id%
Campaign ID - this will insert unique identifier of the report, that you are sending to.