Se il biglietto costa troppo, andiamo a piedi.

Se means if. It introduces the condition:

Se il biglietto costa troppo = If the ticket costs too much / If the ticket is too expensive

This is a very common way to build conditional sentences in Italian.

Italian uses articles much more often than English. So where English often says the ticket or even just tickets in some contexts, Italian usually wants an article.

Here, il biglietto means the ticket.

• il = the
• biglietto = ticket

Leaving out il would usually sound incomplete or unnatural in this sentence.

Costa is the third person singular present tense of costare, meaning to cost.

The subject is il biglietto, which is singular, so the verb must also be singular:

• il biglietto costa = the ticket costs

Other forms would be:

• io costo = I cost
• tu costi = you cost
• lui/lei costa = he/she/it costs
• noi costiamo = we cost
• voi costate = you all cost
• loro costano = they cost

Here troppo means something like too much in price, so in natural English the whole idea is usually too expensive.

Literally:

• costa troppo = it costs too much

Natural English:

• it is too expensive

So Italian often expresses this idea with costare troppo rather than needing an adjective like costoso.

Because in this sentence troppo is being used as an adverb, not an adjective.

It modifies the verb phrase costa:

• costa troppo = costs too much

As an adverb, troppo does not change for gender or number.

Compare:

• un biglietto troppo caro = a ticket that is too expensive
  Here troppo is still invariable, and caro is the adjective that changes if needed.
• costa troppo = it costs too much
  Here troppo works adverbially.

Andiamo is the first person plural present tense of andare, meaning to go.

So:

• andiamo = we go

In this sentence, it means:

• andiamo a piedi = we go on foot / we walk

Italian often uses the present tense here where English might use will.

Because Italian usually drops subject pronouns when they are not needed.

The verb ending already tells you who the subject is:

• andiamo clearly means we go

So noi is optional. You would add noi mainly for emphasis or contrast:

• Noi andiamo a piedi = We are going on foot

Without emphasis, andiamo a piedi is the normal choice.

This is a very common Italian pattern. In real, possible conditions, Italian often uses the present tense in both parts:

• Se il biglietto costa troppo, andiamo a piedi.

Literally:
If the ticket costs too much, we go on foot.

But in natural English, this is often translated as:

• If the ticket is too expensive, we’ll go on foot.

So the Italian present tense here can correspond to an English future idea.

A piedi is a fixed expression meaning on foot.

So:

• andare a piedi = to go on foot
• venire a piedi = to come on foot

You should learn a piedi as a chunk, because it does not translate word for word in a very natural way.

Because a piedi is just the idiomatic Italian expression. Languages often use prepositions differently, and this is one of those cases.

English says:

• on foot

Italian says:

• a piedi

Even though it may not feel logical if translated literally, a piedi is the standard and correct form.

Sometimes yes, but the meaning is not exactly identical.

• andiamo a piedi = we go on foot
• camminiamo = we walk

In many contexts they overlap, but andiamo a piedi emphasizes the means of getting somewhere, while camminiamo focuses more on the action of walking.

So in this sentence, andiamo a piedi is especially natural because it contrasts with paying for a ticket.

Yes. You can also say:

Andiamo a piedi se il biglietto costa troppo.

That is also correct.

The version with the if-clause first is very common, especially when you want to present the condition before the result:

• Se il biglietto costa troppo, andiamo a piedi.

If the se clause comes first, a comma is commonly used. If it comes second, the comma is usually omitted.

The comma separates the condition from the main clause:

• Se il biglietto costa troppo = condition
• andiamo a piedi = result

When the if-clause comes first in Italian, using a comma is normal and helpful for clarity.

Yes, absolutely.

• Se il biglietto costa troppo = If the ticket costs too much
• Se il biglietto è troppo caro = If the ticket is too expensive

Both are natural. The first focuses on the cost, while the second uses the adjective caro meaning expensive. In everyday speech, both work well.

Not necessarily. Biglietto can refer to many kinds of tickets, such as:

• a train ticket
• a bus ticket
• a cinema ticket
• an entry ticket

The exact type usually depends on context. In this sentence, it simply means the ticket.

Yes. It is a very useful basic pattern:

Se + present tense, present tense

Example:

• Se piove, restiamo a casa. = If it rains, we stay home / we’ll stay home.
• Se ho tempo, ti chiamo. = If I have time, I call you / I’ll call you.

This is one of the most common everyday conditional patterns in Italian.