To being with, you first need to keep in mind that forms are of different type of content than text areas or galleries. You can build any kind of forms, also those which include large bodies of texts in them, but forms themselves are managed separately from other content areas.
To create a new form, first open the '+Add tab on the lower menubar. Now drag&drop 'Form' content on your page where you would like your form to appear. The form created is a default one but you can change, remove or add fields and texts any way you please.
Also, the general settings of your form are set as default. To change them, click on the cogwheel icon on the upper left corner of your form. From there, you can change various settings of your form, including the text on the button, confirmation messages etc.