i won a bid on an iphone 6s 64gb on ebay . i do...

iCloud locked

Yes, it is a problem. It means you cannot activate the phone without the Apple ID and password of the person who locked it, and it cannot be bypassed.

It’s locked to a specific Apple ID and can only be activated by logging into it. Unless you’re able to get the seller to remove the lock, you won’t be able to use that iPhone.