In frigo c’è del salmone per cena, ma io preferisco dei cracker con un po’ di salame.

Both are possible, but in frigo is very common in everyday Italian and sounds natural, like saying in the fridge in English.

A few useful points:

• frigo is the short form of frigorifero
• in frigo is a very common idiomatic expression
• nel frigo is also correct, but can sound a little more specific or literal

So In frigo c’è... is a perfectly normal way to begin the sentence.

C’è means there is.

It is the contraction of:

• ci = there
• è = is

So:

• c’è del salmone = there is some salmon

This ci is not the pronoun meaning us. In this structure, it is part of the expression used to say that something exists or is present somewhere.

Because del salmone is treated as a mass noun, not as a countable plural item.

Italian uses:

• c’è for singular or uncountable things
• ci sono for plural countable things

So:

• C’è del salmone = There is some salmon
• Ci sono dei cracker = There are some crackers

Even though the English translation may use some in both cases, Italian still distinguishes between uncountable singular and countable plural.

Here del means some.

It is a partitive article, formed from:

• di + il = del

With food, Italian very often uses these forms to mean an unspecified quantity:

• del salmone = some salmon
• del pane = some bread
• del vino = some wine

English often leaves this idea less visible, but Italian usually marks it.

Dei also means some, but it is used with plural countable nouns.

It comes from:

• di + i = dei

So:

• dei cracker = some crackers

This is different from del salmone, because cracker is countable, while salmone here is an uncountable food substance.

Also, cracker is generally invariable in Italian:

• un cracker
• dei cracker

The singular and plural form of the noun stay the same.

Because these are three different ways of expressing quantity.

• del salmone = some salmon
• dei cracker = some crackers
• un po’ di salame = a little salami / a bit of salami

Un po’ di is a fixed expression meaning a little bit of. After it, Italian uses plain di, not a partitive article.

So you do not say:

• un po’ del salame in this meaning

Instead you say:

• un po’ di salame

Because po’ is a shortened form of poco.

The apostrophe shows that part of the word has been dropped. So the correct spelling is:

• un po’

Not:

• un pò

That accented form is a very common misspelling, but standard Italian uses the apostrophe.

Yes, Italian often drops subject pronouns because the verb ending already shows the subject:

• preferisco already means I prefer

But io is included here for emphasis or contrast:

• ..., ma io preferisco... = ..., but I prefer...

The idea is something like:

• There is salmon for dinner, but I personally would rather have...

So io is not necessary for grammar, but it adds contrast and makes the sentence sound more pointed.

Per cena means for dinner.

Here per expresses purpose or intended use:

• del salmone per cena = some salmon for dinner

It tells you what the salmon is meant for. It does not mean during dinner in a strict time sense; it means the salmon is intended as the dinner food.

Italian often puts location first when setting the scene.

So:

• In frigo c’è del salmone...

feels natural because it first tells you where the salmon is, and then tells you what is there.

You could also say:

• C’è del salmone in frigo...

That is also correct. The difference is mainly one of focus and rhythm:

• In frigo c’è... = starts with the location
• C’è... in frigo = starts with the existence of the item

Both are natural.

Because preferire means to prefer, that is, to like one option more than another.

The sentence contrasts two possibilities:

• salmon for dinner
• crackers with a bit of salami

So preferisco fits perfectly because the speaker is choosing one option over the other.

Compare:

• Mi piacciono i cracker = I like crackers
• Preferisco dei cracker = I’d prefer some crackers

So preferisco expresses preference, not just general liking.