Im working as an independent contractor. I just bought toner for my printer, how do I record it in Quickbooks?

Long story short, my old company hired me to do a job for them. I used to be an employee but this is as an independent contractor. I downloaded Quickbooks Simple Start to keep track of what I spend on the job. I put the job as an invoice in quickbooks. I want to put the expense somewhere, but when I tried putting a cash expense it said I cant have a negative balance. I'm just using my own personal money. Do I add a transaction somewhere where I pretend I added money to the business, then spent it on the toner? I'm new at all this so I just want to know the correct procedure. Thanks.