DOs and DON'Ts for overweight people

Hello! I'm a 34-year-old, ~ 140 kg (308 lbs) blob of fat. Recently I started going to the gym for the first time in over 15 years. As a terribly overweight and terribly unfit person, what should I focus on and what should I avoid? For example: squatting - with weights, only body weight, or no squatting at all? I'll be grateful for any tips! Wishing everyone a nice day!