There are a few ways of adding user variables in the visual email editor. First and the simplest way is inserting variables from the menubar. If you're using custom data, your custom variables will appear in the list as well.
Alternatively, you can add fallback attributes. They are useful in cases, when your database is a mix of registered customers (personal info you have) and annonymous visitors named as 'focused iguana', 'pedantic racoon' etc...
In order to avoid cases when some users receive your email starting with "Hi Pedantic racoon!" ... 😬, we recommend using fallback attibutes
{first_name, "ENTER FALLBACK HERE"}
For example, Hi {first_name, "there"}!) will be resolved as "Hi David!" in case if you have customers' name, or "Hi there!" in case of the anonymous visitor.