Forms can be used for almost any purpose of collecting data such as: a subscribe form, survey form, RSVP form, update profile form, unsubscribe form, etc.
Form Overview Video below:
Once a list has been created you will find 4 default forms automatically created against that list:
subscribe form - which functions as a means of collecting data. This type of form can also be used for many other purposes such as a survey or RSVP
update profile form - which functions as a means of adding or editing data you already have. This form can also be used when sending a survey to contacts you already have to update the new data against
unsubscribe form - only has one purpose which is to flag the contact that fills in the form as unsubscribed
You can also add in and delete as many forms as you wish in the lists. For further information on adding new forms, please refer the article called 'Adding a new Form / update profile / survey to a list'.