What is JotForm?
JotForm is a free online form builder which helps you create online forms without writing a single line of code. No sign-up required.
At JotForm, we want to make sure that you’re getting the online form builder help that you need. Our friendly customer support team is available 24/7.
We believe that if one user has a question, there could be more users who may have the same question. This is why many of our support forum threads are public and available to be searched and viewed. If you’d like help immediately, feel free to search for a similar question, or submit your question or concern.
Here's a sample form I just created for you as an example https://form.jotform.com/70435404599966
This form has 3 fields, one field is hidden with label Hidden Field. When you submit this form, it would redirect back to the form (as an example) and populate the email and hidden box fields.
To add a hidden field, just search hidden box field in the widgets tab and add it in your form.
You can also add a regular textbox field and hide it by going to the field properties > advanced > hide field.
And to add your custom thank you URL, here's how:
If you want to capture the form data after submission and post it on your website or your custom URL, you need to use post method to achieve this. This requires basic knowledge with PHP. Guide: https://www.jotform.com/help/213-Send-Submission-Data-via-Post-Method-and-Thank-You-Settings
If you need further assistance or if this is not what you mean, let us know so we can further help you.