To automatically create a new task from a Submitted Form, you will need to add a Form Action to either an existing Form Template or a new Form Template.
To add this action to an existing form, in the Web Portal select Forms > Existing Forms > select the Edit Arrow on the Form you would like to add the Action to > Actions > + New Action,
Select Create CRM Task from the Action Type Drop down Box and fill in the details for the specific Task that you would like to be completed once the Form has been Submitted. Then Save Actions at the bottom of the page.
This can also be set up in conjunction with Form Conditions to ensure the action is triggered when the requirements are met. For example; this can be triggered upon answering a question in the form like a Yes / No, the condition would require that question to have a specific answer (Yes or No) for the task to create upon submission.