ME3 MP Challenges: I don't get it...
Welcome to the game!
You can check your Challenges status in-game, or via the nifty PC N7HQ website. I took the liberty of looking up yours (assuming this is you, playing on PC):
Look at the Overview and Challenges pages. Also, the Inventory is a great way to check out what stuff you've acquired. And the Character page lets you see all your builds.
In-game, it is the last entry on the main MP screen. Note: you cannot access Challenges when in a lobby (maybe a smart move by Bioware to keep people from wasting their squadmates time).
Most of them are self-explanatory. For most, you just use the specified gun, or power, and get points by damaging and/or killing enemies with them. They are grouped in "Mastery's" which require you to complete X (out of Y available) of each set to get the extra Mastery challenge completion. For character-based ones, it is either get game extractions, or just complete X waves while playing that character. For Map Mastery/challenges, complete waves on those maps.
The one you mentioned, promotions, counts towards the N7 Mastery (and also increases your N7 Rank, a separate rating from the Challenges rating).
So basically, grind, grind away and you'll start completing challenges. It is set up to ( a ) keep you playing and (b) entice you to try different kits, powers, difficulty levels.
Enjoy!
