You're going to have to be really dedicated to actually get stronger. It's going to suck for the first few months, but the only way it's going to get better is for you to push and don't stop pushing until you meet your goals.
I'd say right now with your bodyweight, pushups and situps will easily make noticeable gains for you since you've never really worked out.
To be honest with you, My chest didn't start sticking out until I started doing pushups.
If you want a good program for your abs, I'd suggest the "8 minute abs" They show it on TV all of the time.
If you actually want to buy it you can go on google and type it up and find a website. Or if you're like me, you can find it on any p2p
Believe me, by the end of the 8 minutes your ass is kicked. And if you do that program for a month or more I guarentee your stomach will be a brick wall. If you want to make it harder, do the program, and before you go to sleep knock out 50-100 situps (you can do crunches, but for me, situps work me better)
To give you some inspiration, When I first decided to get in shape I was 230 pounds, Almost all fat. Within maybe 8-12 months I got myself down to 155. And from there I decided it was time for me to put on some muscle. Now I am up to about 173, and I'd say 90+ percent of that weight I gained is muscle.
So it is possible to get in shape. You just have to be dedicated. Don't stop until you meet your goals, Then continue doing what you're doing in order to maintain yourself.