Unfit to fit ASAP? Please?

I'm joining army cadets soon and I'm out of shape due to many different things. How can I get fit fast? I want to increase strength too but it seems to be taking forever in the gum and I'm not getting much muscle? Im not asking to be hench just strong and fit? I have a lot of time off now for nine weeks but I'm joining cadets in a week. Sure I won't be fit for then but I won't need fitness right away. Also I want to join the army and police when I'm older and be apart of physical activity.