登る and 降りる: climbing a mountain and descending stairs
Compare mountain climbing, going down stairs, and getting off a bus, separating direction of movement from reaching the summit.
Moving upward
登る, read のぼる, is used for climbing upward. 週末に山に登りました。 says that someone climbed a mountain on the weekend. Reaching its summit requires separate confirmation.
山の頂上まで登りました。 says that someone climbed as far as the mountain’s summit. Do not automatically add this explicitly stated extent to the first sentence.
Descending stairs or getting off a vehicle
降りる, read おりる, can describe descending or leaving a vehicle. 階段を降りて、受付へ行きました。 says that someone went down the stairs and went to reception.
次の停留所でバスを降ります。 says that someone will get off the bus at the next stop. 階段を marks a descending route, while バスを marks the vehicle left.
The route, object, and extent of movement
山に登ってから、階段を降りました。 says that someone climbed the mountain and then descended the stairs. Keep the movement targets, the mountain and the stairs, distinct.
降りて is the て-form of 降りる and is read おりて here. Unlike ふる in 雨が降る, it describes a person descending or getting off.
What does を identify in 階段を降りました and バスを降ります?
Show the answer and why
In the first, it marks the stairs as the descending route. In the second, it marks the bus as the vehicle left. The same particle accompanies different movement relations.