Subcategory in a form

Hi! I am a beginner! I am working on a form and I stumbled upon a problem: I want to make a subcategory. For example example I have a check box and if the person checks it I want him to fill in a text box, but right away(when he checks the text box should appear, otherwise it should not appear).
For example:
City: (text)
(check)is it on the road?
if/when on the road is checked: which road?(text)
Thank you! :slight_smile:

This can be done with javaScript.

If you are a complete beginner, I would suggest you look into jQuery (, and take a look at their tutorial: