Hi Helena,
Great to see that you have started a journal and I look forward to reading your updates!
Personally I am on the WeightWatchers plan which I have found has worked really well for me but hopefully you will find a plan that fits in with your own lifestyle and works for you. Will you be following any particular eating plan?
The only advice I have re: the gym would be just get started! I was a bit nervous about starting the gym in the beginning but once I made myself go a few times, I really started to enjoy it. Now I make myself go even if I don't feel like it and it's starting to become a good habit.
Best of luck with reaching your diet and fitness goals - I'm sure you will do great
Have a good week.