Aren't essences, serums, and ampoules all the same?

I've been browsing online shopping malls lately to replace my basic skincare products, but there are so many types of essences, serums, and ampoules that I'm having serious trouble deciding what to buy. They all look pretty similar, but since every brand has a different name for them, I felt like my head was going to explode trying to figure out which one would actually suit my skin. At first, I thought they were all just the same type of nourishing essence, differing only slightly in consistency from wateriest to thinnest. But after searching online, I just started getting even more confused...

My skin has been really dry and dull lately, so it's the perfect time for intensive care. I've heard that ampoules work faster because they are the most concentrated, but I'm also wondering if serums or essences might be better for daily use without feeling heavy... Which one would be best for my skin?