I always figured that hops=bitter=higher abv%
Like distantmantra said, ABV depends on the amount of fermented sugars. So if you wanna drive up the ABV, you need more sugar and usually end up with residual sweetness.
Try some Belgian quadrupels or (English) barleywines to taste for yourself.
Bitterness (and other flavors) comes from the hops. Bitterness can be measured too (in international bitterness units/IBUs), which you'll sometimes find on the labels.
Problem is that these IBUs will only give you a rough estimate of the bitterness you taste, as it depends on other factors, mostly the aforementioned residual sugars (and maybe also the alcohol). For instance, an (American style) barleywine with about 70 IBUs and maybe 11% will usually still taste mostly sweet, an IPA with the same IBUs will taste pretty bitter, and a drier, lower alcohol style like maybe a pilsener would probably be undrinkable with that amount of bitterness.
This also kinda explains why there has been a trend of increasing the ABV level especially in America, as it will give you more body and a malt backbone for a full blast of hops with all its desirable aroma and flavor. And it explains why trying to recreate that same hoppy flavor in lighter "session" beers fails so often.
tl:dr: Try all kinds of beers instead of reading my nonsense. You'll figure it out easily enough.