Okay, I just got a bike yesterday and its nothing but a cheapie from Target. I have realized I'm woefully out of shape. Are there any tips for getting in shape quickly?

I bought a wide seat since the seats that come standard always make me sore. This one is still making me sore. Is it just getting used to it or is there something I should do differently?

And this is the height of my stupidity, what gears are for when? Are the harder gears for going up hill or down or for flat?

And please tell me I will get to wear I can pedal up hill with my son in the trailer! Goodness, I could hardly get up the hills!