As others of said, start by just doing something. In a way, it is similar to coding in that you don't have to know every detail of a language before starting to program.
But with respect to your questions:
You can figure out how many calories you can eat based on your gender, age, and weight by calculating your TDEE (various calculators can be found online. Advice I've heard is to tell it that your activity level is sedentary since those calories can often be overestimated.)
I have spent a lot of time researching improving my health over the past year (and have done so) and found the reddit fitness FAQ (http://www.reddit.com/r/Fitness/wiki/faq) to be very educational and reasonably short. Highly recommended that people read it.
You may also want to check out the myfitnesspal (or similar) mobile app which helps you track your calories. I personally just google foods and use a text file but many people like the app.
But with respect to your questions:
You can figure out how many calories you can eat based on your gender, age, and weight by calculating your TDEE (various calculators can be found online. Advice I've heard is to tell it that your activity level is sedentary since those calories can often be overestimated.)
http://www.eatthismuch.com is a website that will plan out meals for you based on calories.
I have spent a lot of time researching improving my health over the past year (and have done so) and found the reddit fitness FAQ (http://www.reddit.com/r/Fitness/wiki/faq) to be very educational and reasonably short. Highly recommended that people read it.
You may also want to check out the myfitnesspal (or similar) mobile app which helps you track your calories. I personally just google foods and use a text file but many people like the app.