The MiFi 4510L must have an active account and 4G SIM card to work correctly. However, you can use the router only/LAN functionality with this device without the SIM card.
Unless someone was kind enough to leave the device activated and will pay your monthly charges then you will need to activate your own SIM card to get on the internet. A retail store should be able to help you in this area. Otherwise the 1800 number for Verizon can also send you a newly activated SIM card too.