Out of shape newbie

Hello there. I'm Heather, 26 and very out of shape. Even small tasks like walking get me sweaty and winded I can't even do a real push up. I'm at the desk all day and haven't been truly active since I played sports in elementary school. I guess my goals are to start building my endurance up and to gain some strength. Ten or fifteen pounds off wouldn't be too bad either. I want to be sporty and athletic, able to keep up with other people my own age.