What if the buyer didn't pay on Ebay?

I sold an iPhone 4 for $180 and I received an invoice for $18. I paid Ebay already with my debit card, even though I haven't gotten any type of payment from the buyer. I sent them an invoice, but I don't know what else I'm supposed to do. I've never sold anything before.

Also, if I don't have a PayPal account, will the (eventual) payment form the buyer be directly credited on my debit card since its my only method of payment on my account? PayPal is too confusing to me.

Added (1). *from

Strange, in the UK a seller MUST offer paypal as a means of payment. Paypal is actually quite straight forward.