Is there a way to save an incomplete form before submitting ?

I have created a big form that I want to use  for people to apply for my service, I want to know if there is a way to save the form while filling it up so you can continue to work on it later. 

Yes, we have the feature. In fact, we have two methods:

1. Autofill (https://www.jotform.com/help/227-How-to-Enable-Auto-Fill-Feature).

2. Session URL (https://www.jotform.com/features/save-and-continue/).

Autofill will save the data in the local browser storage so submitters are required to continue later on the same device and browser. If you want to give users the option to continue later using any browser/device, the session URL is recommended.