We'll need more details on this in order to help:
- Which Mac do you have?
- What MacOS are you running? (Apple Menu-->About This Mac will tell you these first two)
- Was the refurbished Mac properly prepared for sale? (Does it start up with the Setup procedure?)
- Are you transferring from a PC or Mac (or not from any computer at all?)
- Do you have iCloud set up on your iPhone, and are your photos, contacts, calendar all synced with iCloud?
- Where exactly did you run into issues, and can you provide details describing the error message you got?