Marta porta l’insalata in una grande insalatiera blu e lascia i piatti nello scolapiatti.

Because insalata starts with a vowel, Italian normally drops the final vowel of la and uses an apostrophe:

• la + insalata → l’insalata

This is called elision. It happens very often with singular articles before vowels:

• l’acqua
• l’amica
• l’idea

So l’insalata simply means the salad.

Porta is the third-person singular form of portare.

Here it means something like:

• brings
• carries
• takes

The exact English choice depends on context. In this sentence, Marta porta l’insalata in una grande insalatiera blu suggests that Marta is bringing/carrying the salad into a large blue salad bowl or serving it in that bowl.

So:

• portare = to carry / to bring / to take

Italian often uses one verb where English might choose different ones depending on perspective.

Here, in means into / in / inside, depending on how literally you want to translate it.

So:

• in una grande insalatiera blu = into a large blue salad bowl / in a large blue salad bowl

Italian uses in very naturally for putting something inside a container.

Examples:

• mettere il latte nel bicchiere = to put the milk in the glass
• versare l’acqua nella bottiglia = to pour the water into the bottle

In your sentence, the idea is that the salad ends up inside the bowl.

Italian adjective position is more flexible than English, but some patterns are very common.

In this phrase:

• grande comes before the noun
• blu comes after the noun

That sounds very natural in Italian.

Why?

• grande is one of those adjectives that often comes before the noun, especially in everyday speech.
• blu is a color adjective, and color adjectives usually come after the noun.

So:

• una grande insalatiera blu = a large blue salad bowl

You may sometimes see different adjective placement in Italian, but this order is the most standard and natural here.

Yes, grande does agree with the noun, but its singular form is the same for both masculine and feminine:

• un grande piatto = a large plate
• una grande insalatiera = a large salad bowl

The plural changes:

• grandi

So:

• una grande insalatiera
• due grandi insalatiere

That is why you see grande with feminine insalatiera.

No. Blu is an invariable adjective, so it stays the same:

• un piatto blu
• una insalatiera blu
• piatti blu
• insalatiere blu

Unlike adjectives such as rosso/rossa/rossi/rosse, blu does not change form.

Insalatiera means salad bowl.

It comes from insalata (salad) plus the suffix -iera, which often refers to a container or object associated with something.

It is a feminine singular noun:

• una insalatiera
• le insalatiere

So in the sentence:

• una grande insalatiera blu = a large blue salad bowl

Piatti is the plural of piatto:

• il piatto = the plate
• i piatti = the plates

The article i is the masculine plural definite article used with most nouns that take il in the singular.

So:

• il piatto → i piatti

In the sentence, i piatti means the plates.

Yes, lascia literally means leaves, from the verb lasciare.

But in this kind of everyday sentence, it can also mean:

• puts down
• leaves in
• sets

So lascia i piatti nello scolapiatti means that Marta leaves/puts the plates in the dish rack.

Italian often uses lasciare in contexts where English might prefer put or leave depending on the situation.

Because in + lo contracts to nello.

So:

• in + lo scolapiatti → nello scolapiatti

Italian normally combines certain prepositions with definite articles:

• in + il = nel
• in + lo = nello
• in + la = nella
• in + i = nei
• in + gli = negli
• in + le = nelle

You use lo here because scolapiatti begins with s + consonant (sc-), and nouns with that kind of beginning take lo in the singular:

• lo scolapiatti
• lo studente
• lo specchio

So nello scolapiatti is the correct form.

Here scolapiatti means dish rack or drainer.

Even though it ends in -i, it is often used as a singular noun in this meaning:

• lo scolapiatti = the dish rack

It is a compound word:

• scolare = to drain
• piatti = plates

So it literally suggests something like plate-drainer, but the natural English translation is dish rack or draining rack.

That is why the sentence has:

• nello scolapiatti = in the dish rack

Because the sentence treats them differently:

• una grande insalatiera blu = a large blue salad bowl
  This is indefinite: one bowl, not specifically identified beforehand.
• nello scolapiatti = in the dish rack
  This is definite: a specific dish rack, probably the one in the kitchen.

So the contrast is:

• una = a/an
• nello = in the

This is the same kind of difference English makes between a and the.

Yes. Marta is the subject of both porta and lascia.

Italian does not need to repeat the subject if it stays the same:

• Marta porta l’insalata ... e lascia i piatti ...

This means:

• Marta brings/carries the salad ... and leaves/puts the plates ...

Repeating Marta would be possible for emphasis, but normally it is unnecessary.