I'm So Out Of Shape!!

I used to Ice skate, I was a competitive figure skater. Then I started getting pain in my knees, so I decided I needed to go to a doctor, despite the fact that I'm TERRIFIED of them. So we went to the knee&leg specialist and he xrayed my knees. He told us that I have Bursitus [might have spelled that wrong] and that I needed to do physical therapy to heal it. I did and it worked! And I was in shape! But over the 4 months it took me to heal I didn't go to the rink once. Now I loved skating, I skated for the majority of my life, starting at the age of 4. I still love skating, I miss it terribly! Anyway, Because I didnt go for a long time I just stopped going altogether. Bad idea! I'm terrible at all sports excluding skating, Iv'e tried almost all the sports I can think of. So I havent gotten much exercise in the past 3 years since I stopped skating. So I need to start exercising again before I end up looking like my fat lard of a brother. I have no idea where to start! And I'm very limited. I don't drive so I can't go to a gym or anything. Has to be at home or in the neighborhood. I really wanna lose 20 pounds. And get flat abs. If you have any suggestions on how to get flat abs lemme know! Well I'm off to ponder what to do tomorrow. :)