If you're just starting and you're not flexible, then I think you just gotta stick to it and you'll notice little improvements over time. When I started I thought I will never touch my toes without struggling and I just did basic stretching and it's already really noticeable. So consistency is very important.
The way I know that the stretch worked, your body will feel loose, and relaxed and if you feel the burn. If you’ve ever had pain anywhere that has been bothering you, stretch that part out the most, and soon hopefully it will stop bothering you. Stretching helps your body to heal faster and better!