Q: how do I link my iPad to my iphone

You need 3rd party apps like iTransfer if you intend to transfer files.

https://itunes.apple.com/sg/app/itransfer-share-files-ease/id480195086?mt=8

AirDrop can be used with iPhone 5 or later, iPad 4, iPad Mini and iPod 5.

http://support.apple.com/kb/ht5887

What does "link to your iPad" mean to you? You can't link the two devices with a cable, you can't sync the two devices with a cable, in short you can link them in any conventional sense.

If you want to keep the devices in sync with regard to notes, reminders, calendar events, photo stream, app, music and book downloads, you can do that in iCloud Settings and iTunes and App Store settings.

What are you trying to do?

iOS: Understanding Personal Hotspot

http://support.apple.com/kb/HT4517

Use Bluetooth to tether your iPhone, iPod touch, or iPad

http://www.macworld.com/article/1159258/bluetooth_tethering.html

How to Connect an iPad to an iPhone Via Bluetooth Tethering

http://techtips.salon.com/connect-ipad-iphone-via-bluetooth-tethering-25472.html

 Cheers, Tom