На лестнице много ступенек, и я медленно поднимаюсь по каждой ступеньке.

In Russian, на is used with many surfaces or “open structures” where English might say “on” or “on the stairs”:

• на лестнице = on the stairs / on the staircase
• на улице = in the street / outside
• на балконе = on the balcony

В is used more for being “inside” a closed space:

• в комнате = in the room
• в доме = in the house

A staircase is seen as something you are on, not inside, so на лестнице is the normal choice.
В лестнице would sound wrong in this context and is practically never said.

Лестнице is in the prepositional case, singular.

• Nominative (dictionary form): лестница (a staircase)
• Prepositional singular: о лестнице, на лестнице

After the preposition на in the meaning “on/at (location)”, Russian usually uses the prepositional case:

• на столе (on the table) – from стол
• на улице (in the street) – from улица
• на лестнице (on the stairs) – from лестница

So the ending -е here marks “on the staircase” in a static location.

Because много (“many, a lot of”) requires the genitive plural.

The noun here is ступенька (a step, little step). Its genitive plural is ступенек.

General rule:

• After много, мало, несколько, сколько, you use genitive plural:
  • много книг (a lot of books)
  • мало людей (few people)
  • несколько стульев (several chairs)
  • много ступенек (a lot of steps)

Много ступеньки or много ступенька is ungrammatical.

Ступенек is the genitive plural of ступенька.

Declension of ступенька:

• Singular:

  • Nom.: ступенька
  • Gen.: ступеньки
  • Dat.: ступеньке
  • Acc.: ступеньку
  • Instr.: ступенькой
  • Prep.: ступеньке

• Plural:

  • Nom.: ступеньки
  • Gen.: ступенек
  • Dat.: ступенькам
  • Acc.: ступеньки
  • Instr.: ступеньками
  • Prep.: ступеньках

The genitive plural ступенек drops ьк and uses -ек, which is a common pattern for feminine nouns with -ька/-енька in the singular. It’s irregular-looking but very standard.

Both can mean “step (of a staircase)”, but:

• ступень – more neutral, “a step” (feminine noun)
• ступенька – a diminutive, often implying:
  • small size,
  • or a more informal, “everyday” tone.

In many everyday contexts, Russians naturally say ступенька for the steps in a staircase, especially when picturing physical steps under your feet.

Examples:

• На лестнице много ступеней. – completely correct, a bit more formal / neutral.
• На лестнице много ступенек. – very common in colloquial speech; feels more “concrete,” like you see the little steps.

Your sentence uses ступенек, so the tone is everyday, slightly more “visual/physical.”

In по каждой ступеньке, the preposition по governs the dative case:

• каждая ступенька (Nom.)
• по каждой ступеньке (Dat.)

One of the main uses of по is to show movement along / over / on the surface of something:

• идти по улице – to walk along the street
• подниматься по лестнице – to go up the stairs
• бегать по пляжу – to run along the beach

So:

• поднимаюсь по каждой ступеньке literally: “I’m going up on each step,” moving step by step along them.

That’s why по requires the dative (каждой ступеньке), not accusative or genitive, in this meaning.

In Russian, каждый / каждая / каждое (“each, every”) is always followed by a singular noun, even if the meaning is “each one of many”:

• каждый день – every day
• каждая книга – each book
• каждый студент – each student
• по каждой ступеньке – on each step

The idea is: you consider the steps one by one, and каждый selects a single element from the set.

So grammatically:

• каждая ступенька (Nom. sg.)
• по каждой ступеньке (Dat. sg., after по)

Plural would sound wrong: по каждых ступеньках is ungrammatical here.

Поднимаюсь is the 1st person singular present of the reflexive verb подниматься.

• Infinitive (impf.): подниматься – to go up, to ascend, to get up
• Я поднимаюсь – I am going up / I am climbing

The -сь (or -ся) ending marks the verb as reflexive.

Compare:

• поднимать = to raise, to lift (something)
  • Я поднимаю коробку. – I am lifting a box.
• подниматься = to rise / to go up oneself
  • Я поднимаюсь по лестнице. – I am going up the stairs.

So поднимаюсь means you yourself are moving upward, not lifting something else.

Aspect choice:

• подниматься (impf.) – focuses on the process, repeated or ongoing action.
• подняться (pfv.) – focuses on the result or a single completed action.

Your sentence:

…и я медленно поднимаюсь по каждой ступеньке.

This describes the action as it is happening, step by step, slowly. So the imperfective is natural.

If you used the perfective:

• …и я медленно поднялся по каждой ступеньке.

This would emphasize that the action is completed (“I slowly went up (all the steps)” – done). It’s possible, but it changes the feel from “I am climbing, step by step” to “I climbed (and finished climbing), step by step.”

Yes, you can say поднимаюсь по лестнице. It’s very common and fully natural.

Differences:

• поднимаюсь по лестнице – I am going up the stairs (general route)
• поднимаюсь по каждой ступеньке – I am going up each step, step by step, emphasizing:
  • the individual steps,
  • and often the slowness or effort.

So:

• На лестнице много ступенек, и я медленно поднимаюсь по лестнице.
  → Neutral description: there are many steps; I’m slowly going up the stairs.

• …и я медленно поднимаюсь по каждой ступеньке.
  → Draws attention to every single step; feels more vivid, maybe tiring or careful movement.

Both are correct:

• я медленно поднимаюсь
• я поднимаюсь медленно

They mean the same thing: “I go up slowly.”

Differences are subtle:

• я медленно поднимаюсь – slightly more neutral; медленно comes earlier, coloring the whole action that follows.
• я поднимаюсь медленно – often gives a bit more emphasis on how you are going up (slowly), as if contrasting with another way (quickly, for example).

In everyday speech, both orders are natural. Russian word order is relatively flexible, especially with adverbs like медленно.

In Russian, the comma rules are stricter than in English.

Here we have two independent clauses:

1. На лестнице много ступенек – There are many steps on the staircase.
2. я медленно поднимаюсь по каждой ступеньке – I am slowly going up each step.

They are joined by и (“and”), so Russian requires a comma:

• На лестнице много ступенек, и я медленно поднимаюсь по каждой ступеньке.

If и joined just two words or two short phrases inside one clause, there would be no comma:

• много длинных и узких ступенек – many long and narrow steps (no comma)

But between full clauses with their own subjects and verbs, you normally put the comma before и.