First, happy National Homebrew Day celebration day. I hope you have a LHBS or club that is participating in the Big Brew.
Gravity is a measure of sugar in your wort, and the more fermentable sugars you give your yeast to munch on, the more that yeast will pee alcohol. To get gravity without booze, you provide yeast more of the stuff they can’t consume.
From the first recipe I created without looking to clones or other recipes, I learned that the greater the malt, the fewer the fermentables. For instance, pilsner malt offers more potential fermentable sugar than a dark crystal malt. A brew heavy on crystal malts should have little alcohol and plenty of flavor, mouthfeel / body, and color. That’s something Beer Smith assumed I would understand… but itself does not understand when calculating ABV.
In all-grain brewing, controlling the time and temp of your mash helps determine what sugars are available. “How To Brew” and “Designing Great Beers” have great intro info about that process. Other types of sugars, like lactose used in “milk stouts,” add body without booze.
Finally, adjuncts (maybe not the right word in this case) like oats or wheat will also add to the body, creaminess, and head retention.
The best way to figure it out is to research the recipes and process of the beers you enjoy. That’s done on some breweries’ websites, by calling the breweries, or by looking for clone recipes.