A word of advice to anyone new to the fitness world or starting over again. This is the time of year when everyone starts off with good intentions to get in shape, stay fit or compete in a race.
My advice is to RELAX.
No matter where you are in your fitness journey, remember that it takes more time to get back in shape than it did to get out of shape. If you never have please don't start off expecting to compete with someone who has been doing it for all along. I don't know the statistics but I have seen my share of people spend good money and then leave after a few weeks because they didn't see results right off.
Everybody has a body that has been through different stresses and conditions. Take the time to assess where you are (realistically) before you start. Then, if needed consult an experienced trainer to help. Set short and long term goals to achieve. Reward yourself when you reach each goal. Finally, if you don't enjoy what you are doing is it really worth it? There are too many ways to workout to do something that doesn't work for you.
Just find one and DO IT.