You could start your workout routine with some basic, at-home, bodyweight stuff to start building some strength and endurance, and then transition this into a more structured lifting program. You can't just jump into the gym full-force if you aren't prepared for it. Start by building yourself up to it. Good bodyweight stuff includes, lunges (can try while holding heavy things), push-ups and sit-ups of various types, prisoner squats, ect. I'm sure you can think of several others to include as well. DEFINITELY get out and go for long walks regularly. Try to add in about two or three hours of light cardio (55-70% of max heart rate) per week if possible.
As for diet, listen to your body. Eat to satiety and try to learn when that is. You body will tell you. Also, cravings for certain foods may mean that your body needs the nutrition it is offering. If you find you have a craving for protein lately, it may mean that you are not getting enough of it. On the other hand, we all know what sugar and wheat and the like can do to mess up our cravings, so do keep that in mind when trying to figure out what your body is telling you. Lower carb means more rapid fat-loss for most people but this does not always translate to better health. Some people thrive on low or even very low carb diets, other people don't feel well and require more carbohydrates to feel at their best. It is important to experiment with your diet and learn where you feel best. No one can tell you "low carb is bad for you" or that "high carb is evil." You must learn where your body personally feels best. There is no right or wrong here, there is only "I feel great eating the way I do." That is the goal with your diet. Everyone has very individual needs given their genes, body-type, exercise routine, type of job (active or desk-based), ect.