El indicio está junto a un símbolo.

Because this sentence is talking about location.

In Spanish, estar is used for where something is:

• El indicio está junto a un símbolo. = The clue/indication is next to a symbol.

Ser is generally used for identity, description, origin, and other more permanent-type information:

• Es un símbolo. = It is a symbol.

A useful shortcut is:

• ser = what something is
• estar = where something is / how something is

So here, since the sentence tells us where el indicio is located, está is the correct choice.

Junto a means next to, beside, or close to.

So:

• junto a un símbolo = next to a symbol

It is a very common expression for physical position.

Similar expressions:

• al lado de = next to / beside
• cerca de = near

Example:

• La mesa está junto a la ventana. = The table is next to the window.

Because junto normally appears in the fixed expression junto a when it means next to.

So you usually learn it as a chunk:

• junto a = next to

It is not the personal a here. It is just part of the expression.

Examples:

• Está junto a la puerta. = It is next to the door.
• Estoy junto a mi amigo. = I am next to my friend.

This is the difference between the and a/an.

• el = the
• un = a/an

So:

• El indicio = the clue / the indication
• un símbolo = a symbol

This suggests that the speaker is referring to:

• a specific clue already known to the listener: el indicio
• one symbol, not a specific previously identified one: un símbolo

If both were specific, you could say:

• El indicio está junto al símbolo. = The clue is next to the symbol.

Yes, indicio is masculine, which is why it uses el.

• el indicio
• un indicio

Many Spanish nouns ending in -o are masculine, so that is a useful clue, though not an absolute rule.

Likewise:

• símbolo is also masculine
• el símbolo
• un símbolo

So both nouns in this sentence are masculine singular.

The accent mark in está shows which syllable is stressed:

• es-TÁ

It also helps distinguish forms in writing.

Without going too deep, you should simply learn:

• está = he/she/it is or you are (formal), from estar

This accent is part of the correct spelling.

Because the stress falls on the first syllable:

• SÍM-bo-lo

Spanish spelling rules require a written accent here.

So:

• símbolo = correct
• simbolo = incorrect

It is worth memorising the full written form, including the accent mark.

A rough pronunciation guide for Spain Spanish is:

el in-DEE-thyo es-TAH HOON-toh ah oon SEEM-boh-loh

A few useful notes:

• ci in indicio is pronounced like thyo in most of Spain.
• j in junto is a throaty sound, not an English j.
• á and í just show stress; they do not change the vowel into a different vowel sound.

A more syllable-based guide:

• El
• in-di-cio
• es-tá
• jun-to a
• un
• sím-bo-lo

In Latin American Spanish, indicio would usually sound more like in-DEE-syo rather than in-DEE-thyo.

Yes. That would be perfectly natural.

• El indicio está junto a un símbolo.
• El indicio está al lado de un símbolo.

Both mean The clue/indication is next to a symbol.

Very broadly:

• junto a can sound a little more compact or formal in some contexts
• al lado de is extremely common and very natural in everyday speech

Both are correct in Spain Spanish.

Yes, but the original order is the most neutral and standard.

Normal order:

• El indicio está junto a un símbolo.

You might also hear or read variations for emphasis, such as:

• Junto a un símbolo está el indicio.

This version sounds more marked or literary because it highlights the location first.

For most learners, the safest pattern is:

• subject + verb + location

So the original sentence is the best model to follow.

They are related, but not always exactly the same.

• indicio often means indication, sign, or clue
• pista often means clue, especially in detective or puzzle contexts

In many situations, they can overlap. But indicio can sound a bit more formal or analytical, like a sign that suggests something.

Examples:

• La policía encontró una pista. = The police found a clue.
• Hay indicios de fraude. = There are signs / indications of fraud.

So indicio is a good word to learn, but it is not always interchangeable with pista in every context.