How can I put a code or word on the form that allows only those that provide that word able to proceed. Something like a password but not a password?

Yes, this is possible to achieve, you will need to use conditions to do that and here is a guide that will help you with that: https://www.jotform.com/help/316-How-to-show-or-hide-a-field-in-the-form-based-on-the-other-field-input-or-selection.

I would suggest you to avoid using the words passwords or something like that, if you use words like that though your forms are not being used to ask for passwords it may be disabled. 

Hope this will help you.