Hello Sarrah,
If you're using forms 2.0 then Marketo provides code for you to use. Simply navigate to the form, then click 'Form Actions' at the top and select 'embed code'. If you're using 1.0 you can create the form, and either 1.) find the four digit code id, and have them code it in that way, or leave space in the template for you to drag it in from the WYSIWYG.