Qdoba is something like a Mexican "Subway". You come in at one end, look at a menu board of choices - mostly consisting of a variety of burrito choices - and place your order. The primary difference is that no matter what you order off the board, the restaurant operates more like a traditional deli and prices based on what you order, not necessarily what is on the board.
Where a Subway (most fast food places, for that matter) would have particular menu items, at Qdoba you essentially choose what you want and it is priced accordingly - and a number of the items on the menu are simply common configurations of what people may typically order if they put things together on their own. I think it may be less confusing to some if the menu boards were simplified to reflect this.
As to the food, it's pretty decent. You get a good-sized helping, and the price isn't out of line with what you would pay at other fast food places. If you are so inclined, you can eat part of your meal and save the rest for later, which makes it an even better deal. It certainly isn't authentic Mexican, but it's not bad eats when you're pressed for time.