Пожалуйста, покажите пропуск охране у входа.

Покажите is the imperative (command/request) form of the verb показать (to show). Specifically, it’s the polite/plural imperative, used when addressing:

• one person formally (you, polite вы), or
• multiple people (you all).

The informal singular would be покажи.

This is about aspect:

• показать (perfective) = show once / complete the action (what you want at a checkpoint).
• показывать (imperfective) = be showing / show repeatedly or habitually.

At an entrance, you normally use perfective: Покажите пропуск… (Show your pass [now].)

Russian often omits subject pronouns because the verb ending already shows who is addressed. Покажите already signals you (polite/plural), so вы is unnecessary unless you want extra emphasis/contrast.

Пропуск is in the accusative case because it’s the direct object of покажите (show what?).
For an inanimate masculine noun like пропуск, accusative = nominative, so it stays пропуск.

Охране is dative case (to/for someone), because the idea is show something to someone:

• показать (что?) пропуск (кому?) охране.

Охрана means security (as a service/group). If you mean one guard, you could say:

• Покажите пропуск охраннику (dative singular of охранник).

у means by/near/at (location). It requires the genitive case, so:

• вход → у входа (genitive singular).

So у входа = at/near the entrance.

The sentence is natural as-is. Russian word order is flexible, but changes can add emphasis:

• Пожалуйста, покажите пропуск охране у входа. (neutral)
• У входа покажите пропуск охране. (focus on location: “At the entrance…”)
• Охране у входа покажите пропуск. (focus on “the security at the entrance”)

Пропуск is typically an entry pass / access badge / permit—something that allows you to enter a building/area. It’s common in offices, factories, events, or guarded buildings. (A passport is паспорт, and a ticket is билет.)

It’s polite and fairly standard for signs or staff instructions.
Пожалуйста softens the command into a request. You can omit it in stricter/official wording, but it will sound more blunt:

• Покажите пропуск охране у входа. (still normal, just less softened)

Yes. Предъявите пропуск is a very common official/checkpoint phrasing meaning present your pass.
Compared to покажите, предъявите sounds more formal/official (like security or administrative language).

Main stresses:

• пожа́луйста
• покажи́те
• про́пуск
• охра́не
• у вхо́да

Approximate rhythm: Пожа́луйста, покажи́те про́пуск охра́не у вхо́да.