Q: how to transfer contacts from nokia lumia 520 to iphone 5 ?

A lot depends on which email client you use on your computer and what kind of computer (mac or PC).  You have to copy the contacts from your phone to your computer's email client - this depends on the answers to my questions above.  If a PC, then you'll need to wait for someone else to answer.  If a mac, can you get you contacts in the Contacts program on the mac?  Once there you can sync them to icloud then to your iphone, or sync them to the phone using itunes.

Also, does the nokia have a sim card that stored the contacts.  I believe there's a way for itunes or the iphone to import those contacts, but don't recall the process - you might try to google this question to get answers.

You can use SIM Card to solve the issue about how to transfer contacts from Nokia to iPhone.

On your Nokia device select all contacts and transfer them to SIM Card. To do this go to Contacts > Options > Mark All then go to Options > Copy > Copy Contacts to and choose SIM memory .Take out the SIM Card and insert it in your iPhone. Navigate to Settings > Mail,Contacts,Calendar > Import Sim Contacts.

The iPhone 5 uses a nano-SIM versus the micro-SIM in the Lumia 520 so a direct transfer from the Lumia SIM to the iPhone is not possible.

Find out which SIM card your iPhone or iPad uses - Apple Support

http://www.microsoft.com/en-us/mobile/phone/lumia520/specifications/

When I moved from a Lumia 520 to an iPhone 5S I simply went to my local AT&T corporate store and they transferred the Lumia 520 SIM to a new SIM for my iPhone. The new SIM was free from AT&T.