I would like people to add data when the select the option 'other'

In a selection list, people get the option other, but I would like them to specify that answer. How can I make that field fillable in a form?

For the SINGLE and MULTIPLE CHOICE fields, this is the case, where the user types in their OTHER option:

BUT if you want to achieve this on a DROPDOWN field, you can use a hidden SHORT TEXT ENTRY field and condition it to SHOW only when the OTHER option is selected on the dropdown list.

Here is how will the condition look:

And it will function as:

Related user guides:

How to Show or Hide Fields Base on User's Answer

Smart Forms Using Conditional Logic

How to Hide Form Fields

Adding to Scott answer, I have made a sample Jotform so that you can clone it for your use.

https://form.jotform.me/80922818289468