When creating a landing page, to add a form, go to Pre-designed blocks:
Choose Forms and drag and drop the design that you’d like to choose:
When you drag and drop the form, you will see the settings on the left to create a new list or use a previously created list (the previously created list has the fields you’d like to include while the new list created only has the fields shown in the form chosen).
In case you need to add or edit the fields in the form you need to change them from the Form builder. Please check Creating custom form fields for more details.
Once you finish configuring the form settings, click on apply changes:
In case you missed the settings or want to access them again, click on the gear icon: