I am an extreme newbie. I am so new, my bike is still a trail virgin. I need clothing help.

First of all, I don't understand jerseys. Why jerseys and not something else entirely? The ones I have seen in stores seem extremely thin. The jackets I have seen in the stores seem very thin too. Eventhough I live in San Diego, I run cold, so I am worried about buying clothing that will not keep me warm enough. On the other hand, I don't want to be too hot either, once I get going. I am leaning toward capris for the shorts, but I don't want to spend $100 on shorts.

Can anyone make some specific suggestions (brands, items) for layering?

Thanks for any and all help.