We're going to install the 42 tooth giant cog from Wolf Tooth Components. The cog in this video is for a Shimano cassette. We're going to replace the 17 tooth cog and spacer from the cassette and put the giant cog in as a replacement.
First thing to notice is that there are ramps on the cog. This will help you determine the proper direction of the cog. It should be installed with the writing on the cog facing outward away from the spokes of the wheel rim.
The cassette set in this video is an XTR set. The pieces of the cassette are stacked and placed on the hub one at a time. Rather than adding the 17 tooth cog. It is taken out and the 15 tooth goes on the cassette without the 17 tooth next to it. Put the locking on at the end to secure the tightness of the cassette.
The packaging from Wolf Tooth components also comes with a longer B-nut screw to help prevent the derailleur from hitting the giant cog.