URGENT HELP NEEDED!! How do I stretch properly to build muscle tone up?

I've been sick and had major depression for probably the past 4 years. It has come to the point where I have laid in bed and watched tv or slept there 23 hours a day. When I eat, which isnt much, I do it there. The only excercise I get is up and down the stairs a few times a day to step onto the porch to smoke a cig. I know I know. Bad. Anyway....I could use a lecture but I really need to get in shape fast. I need to have a surgery related to cervical cancer within the next 4 weeks and the dr want me to do a physical to see if I am strong enough. I honestly dont. I have never had surgery and am scared of it but it is necessary at this point and I need to get strong so I do not die. I suppose to start off walking would be good but I hate to leave the house. Tonight I tried stretching and the leg muscles are so skinny and not toned at all & can hardly stretch out all the way. It hurts and is tight. Guess they are kind of atrophied. I'm not stupid, just have not cared. What things to do?