Learn Russian: Кафе в двух шагах отсюда.

Russian uses dedicated, single-word adverbs for the direction of origin. You cannot attach the preposition от (from) to static location adverbs like здесь (here) or там (there). Instead, you use отсюда (from here) and оттуда (from there). These act just like откуда (from where) in the spatial correlative clauses you are currently studying.

Why does this sentence use the prepositional case (в двух шагах) to express distance?

In Russian, stating the exact distance at which something is located often uses the preposition в + the prepositional case. You can think of the idiom в двух шагах as meaning "at a distance of two steps." It answers the static location question где? (where?), which is why it triggers the prepositional case here rather than the accusative or genitive.

Doesn't the number два usually take the genitive singular? Why is it в двух шагах?

The rule where два, три, and четыре require the genitive singular only applies when the phrase is in the nominative or inanimate accusative case. Because the preposition в forces this entire phrase into the prepositional case, the number and noun must decline together in the plural. Therefore, два becomes двух and шаг becomes the plural prepositional шагах.