How to track food?

I started gym recently and wanna know how. My BMI is 25.4 currently (which is high) gym trainer said me to regularly visit gym and I sarget 8K steps per day. 6 days gym and 3 days HIIT or Cardio... My BMR in attached image. Wanna lose fat and retain muscles. This is my 4 week workout plan in another image. Gym trainer said me to juat eat home food for a week then he'll explain. But saying home food only isn't enough. I want to know approximation how can I track my food? Mainly Protein? And also tracking calories matters? And how much detailed should it be?