If your device is eligible you can download the title directly on your device through the Windows Phone Store or by using the link which follows:
The game offers a third person perspective and is designed to span a timeline between Halo 3 and Halo 4. However Microsoft promises that you wont have to know the history of the Halo universe to enjoy the game. Those who have played the previous titles may better understand the 25 new missions which offer "new insights into the first missions of the Spartan Ops program, the history of the Human-Covenant wars, and the rise of Commander Sarah Palmer."
Along with the initial cost you can purchase additional credits for in-app purchases of temporary weapon upgrades. The rates range from 500 credits $2.99 to 10,000 for $39.99 credits and since they are temporary upgrades its best save your credit for those levels that are just too hard to pass.