How do I limit a user to enter only a specific number of characters?

ex: i want the form accept the value only if it is of 10 characters. i.e it should throw an error is someone inputs less than or more than 10 characters.

You can achieve this with Textbox field if you set Input Mask. You will also need to check Fill Mask Validation option.

More about Input Masking you can find inside of this guide:

https://www.jotform.com/help/381-Getting-Started-with-the-basics-of-Input-Masking 

Hope this will help. Let us know if you need further assistance.