What is "upload your private key"?

To view my form submissions, I need to upload a private key...what is this?

I have checked and your form is encrypted. When the form is encrypted you will have to upload a private key to decrypt your data. A private key is the key that will decrypt the data. 

When you encrypted your form, key was downloaded to your computer. It is most likely in the downloads folder on your computer. 

If you have lost your key, than you data is also lost. 

More about encrypted forms and how to use them, you can find inside of this guide:

Encrypted Forms and How to Use Them

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