La tarima está junto al atril.

Because the sentence is talking about location.

In Spanish, estar is normally used for where something or someone is:

• La tarima está junto al atril. = the platform is next to the lectern.

Ser is used more for identity, origin, time, material, and other more defining characteristics:

• La tarima es de madera. = the platform is made of wood.
• Eso es una tarima. = that is a platform.

So here, since it says where the platform is, está is the correct choice.

Because the usual expression is junto a, which means next to, beside, or right by.

So:

• junto a + noun
• junto al atril = next to the lectern

By itself, junto often means something like together or appears in other structures, but for physical position with a noun, junto a is the normal pattern.

Because a + el contracts to al in standard Spanish.

So:

• junto a el atril → junto al atril

This contraction is basically mandatory.

The same happens with de + el = del:

• al lado del atril = next to the lectern

One important exception: if El is part of a proper name, you do not contract it:

• Voy a El Escorial.

Because junto here is part of the fixed prepositional expression junto a.

In this use, junto does not behave like an adjective agreeing with tarima. It stays the same:

• La tarima está junto al atril.
• El libro está junto a la lámpara.
• Las sillas están junto a la pared.

So even if the noun is feminine or plural, junto does not change in this structure.

Because Spanish usually uses articles with nouns more often than English does, especially when talking about specific things.

Here:

• la tarima = the platform
• el atril = the lectern

Also, nouns in Spanish have grammatical gender:

• tarima is feminine → la tarima
• atril is masculine → el atril

This gender is a property of the noun itself and does not necessarily have anything to do with biological sex.

In Spain, tarima usually means a raised platform, dais, or sometimes a small stage/platform, often made of wood.

It is not always the same as:

• escenario = a full stage, especially in a theatre or concert setting
• podio = podium, especially for winners or for standing up to speak

So tarima often suggests a slightly raised surface rather than a large performance stage.

Atril usually means a lectern or a stand used to hold something up.

Depending on context, it can be:

• a lectern for a speaker
• a music stand
• a stand for a book or notes

In this sentence, if the meaning shown is something like a speaking area, atril most likely means lectern.

Yes. That is completely natural.

Both of these are common:

• La tarima está junto al atril.
• La tarima está al lado del atril.

They are very similar in meaning.
A small nuance:

• junto a can sound a bit more like right next to
• al lado de is also very common and flexible

In everyday Spanish, both are fine.

The accent mark is necessary because está is a verb form of estar:

• está = is

Without the accent, esta is a different word:

• esta = this (feminine)

So:

• está = verb
• esta = demonstrative/determiner

The accent also shows the stress: es-TÁ.

A rough pronunciation guide would be:

la ta-REE-ma es-TA HOON-to al a-TREEL

A few notes:

• j in junto is the strong Spanish sound, like a throaty h
• r in tarima and atril is a tapped Spanish r
• the stress falls on:
  • ta-RI-ma
  • es-TÁ
  • a-TRIL

So the full sentence is pronounced approximately:

la ta-REE-ma es-TA HOON-to al a-TREEL

Yes, but the original order is the most neutral and easiest for learners:

• La tarima está junto al atril.

You could also say:

• Junto al atril está la tarima.

That version is more marked or literary and may put more focus on the location.

For normal conversation and learning, La tarima está junto al atril is the best pattern to copy.