Since you are new to this you must set up a plan to phase out the bad stuff in your diet and replace it with the good stuff over time. Don't do too much at one time since that may not work for you unless you have a very strong mind.
The same thing applies to a workout regiment. Start by doing basic weight training/cardio routines for a hour 3 -4 times a week and then work from there. As your body becomes accustomed to it then you can start advancing yourself and increasing the time you spend in the gym.
Also educate yourself on what body type you have which will allow you to determine how you will have to train and what foods you will have to eat to achieve the goal you have set up for yourself. If you want to loose weight set up a realistic plan for doing so which you know you can work with and the a different strategy is applicable if you are looking for muscle gains.
Congrats on making this decision and I wish you success on your journey in the world of fitness.