Nokia Lumia 521 - How can I ensure that I will not lose my Contacts information on my Lumia phone?

Your phone will automatically upload the contacts on your phone to the Microsoft account (formerly Windows Live ID) you entered at the initial set up. Whenever in the future you add, remove or amend a contact on your phone, your contacts will be synchronised in the background.

To check your Microsoft account, go to Settings > emails+accounts.