I’ve never used it but recently did some freelance work on a MODx site that was using it. They had it setup as a stand alone application working sibe by side with MODx (not integrated). Once you have the form code you can add it to a chunk (or directly to the content field) and it will ba available on the page. I did not work on the forms (only edited the templates) so I am not aware of any additional steps.
I suspect I’ll be challenged trying to get Form Tools integrated with MODx via SSO. Form Tools is not integrated with any CMS yet that I can find in their forums. Maybe when I get some free time I’ll see if I can get MODx to be the first.