How can I send personalized responses to people that have filled out my jotform?

You should go to the settings tab and email section, once there you will find the emails your form has, either notifications or auto-responder, you will need to simply place the mouse over any of the emails and you will get their options, click on the edit button button to get the email wizard: 

You will get a wizard similar to the one on the screenshot below where you will be able to customize what is sent in the email:

Hope this helps.