A. Halo Reach's weekly and daily challenges are great features that give you extra credits to help with promotions and purchases for your armor.
A great way to see the challenges is via the bungie.net webiste. Go to www.bungie.net, select the Halo Reach icon as highlighted in red, and select Challenges to show the challenges (weekly and daily), along with your progress. The mobile version of the bungie.net site also has the challenges listed for each day.
To view the challenges in the game, press the Start button to bring up the menu and select the Challenges option, as shown here.