Every field has the ability to set a default.
This can be a static value, such as No for a Yes/No radio button.
But it can also be set to leverage a variable. This makes it a dynamic default. It will default to whatever is in that variable.
One common use for this is setting a Requested By field to the user id of the person who is currently logged in using the Identity variables:
But it is also possible to use a bridge to populate the default.
To do this, there must be a bridge set up that has a single result query. This can be a query, for example, of people information that uses the login ID of the individual for a parameter.
The result of that bridge can then be selected from the variables and used in the default.