Nothing can be done through eBay so you and the seller have to work out which method suits you both best.
This can be payment by cheque, bank transfer, of a PayPal Friiends and Family payment. Or, the seller can send you a PayPal invoice.
If PayPal is used, email addresses need to be exchanged, this can sometimes be found with the order details >> Show Contact Info. If not and you need to ask the seller for this, make it very, very clear in your eBay messages, as eBay do read these, the reason for these exchanges. Make it clear it's not to be used for an off eBay sale.
@garderric-0
