You level until level 50. Once 50 you can go to the specialization window and choose which one you want to do first.
All specializations and weapon skins http://halo.wikia.com/wiki/Specializations
During this segment the following happens 1. You cannot go back and change your mind. You must complete all 10 levels before you can change the specialization. 2. Everything is a set order when it comes to unlocking
You gain emblems and backrounds first Level (2-4) You gain the armor (Chest, shoulders, Helmet) Level 5 Is the weapon skin Level 6 Is the specialization visor Level (7-9) Is the armor with a texture skin Level 10 is the actual perk
Official Taokaka supporter! -^w^- http://tousei.deviantart.com/art/TAOKAKA-117133612