When reviewing my return, it is asking me to check this entry "Schedule C: Investment at risk boxes must be entered." What does this mean? Thank you.

When you file a Schedule C, you have to identify whether you're using your own money for the business.

At risk means you're using your own money, or borrowed funds for which you're personally liable, for the business.   A loss may only be deducted up to the amount you personally have at risk.

You must check a box on Schedule C indicating whether or not your business is considered "at-risk."

How do I know which box I should check?
I have only invested my own money, and the loss this year is because of the purchase of new appliances.

You are being about your investment into your business.  You will check Box 32a All investment is at risk.

If you don't know what it means then probably All your Investment is at Risk (check Box 32a). It means you are using your own money for the business.  If you have money not at risk you can not take a loss on schedule C.