How do I know that my baby is getting enough?

My baby is only breastfeeding for 5 or 10 minutes at a time. How do I know they are effectively removing milk from the breast? https://www.laleche.org.uk/signs-effective-feeding-early-days-2/

I can’t tell how much milk my baby is getting… how often should my baby feed in the first few days?

My baby sleeps at the breast all the time