Best Android app for gym newbie?

So I started going to the gym recently. Mostly for the cardio (trying to lose a bit of weight), but I figure while I'm there I might do some weight exercises, try to build up a bit of muscle (not trying to be particularly bulky or anything, but I figure it wouldn't hurt to see if I can get a bit stronger, and hey, it's there).

My problem: I don't really know any exercises. I mean sure there's a few of the machines for certain exercises, those I can figure out, but I wouldn't really know where to begin with free wights. A few times some of the other people there have shown me a few things, but I don't want to have to keep asking for help.

So what I'm looking for is an Android app that, at the very least, has a list of exercises I could do (with instructions, probably diagrams, etc.). What I'd like is if I could get to the gym, open the app, tell it what area/s I want to work on today and how many exercises/how long I want to be there, and it picks some exercises for me and keeps track of how much I can do on them.

I realise what I probably need is a personal trainer - sessions with a personal trainer are a bit out of my price range (as it is, it helps that the gym I'm going to has a student discount). Also on the subject of price, I don't mind paying up front for a good app but I don't want anything with a subscription or a ton of in app purchases.

Anyone got any suggestions? Thanks