Do you have a list of template variables such as {{firstname}}?

Yes, you can click the *add content* link above the content area: 

The following is not a complete list of template variables, because some of them have specific requirements, but here are several of the ones currently available:

• Email - {{ email }}
• First name - {{ firstname }}
• Last Name - {{ lastname }}
• Coupon Code - {{ coupon_code }}
• Item Count - {{ item_count }}
• Phone Number - {{ phone }}
  
• Store URL - {{ store_url }}
  
• Store Name - {{ store_name }}
  
• Order Increment ID - {{ order_increment_id }}
• Date - {{ date }} (The date field can be different things in different triggers.  Example: In the abandoned cart email it represents the quote date while in the order confirmation email it represents the order date).

You can also use twig variables and functions such as:

• {{ "now"|date("Y-m-d_H-i:s") }} - Will show a timestamp.
• {{ firstname ? firstname : "there" }} - If firstname is present it will use it, otherwise it will say "there".  For example: "Hi Bob" vs. "Hi there".
• {{ date|date("M d, Y") }} at {{ date|date("g:ia") }} - May 12, 2016 at 7:05 pm