Passo il brodo nel colino, poi metto la pasta nello scolapasta.

They are both 1st person singular present tense forms:

• passo = I pass / I strain / I run through
• metto = I put

In a recipe or cooking explanation, Italian often uses the present tense to describe steps, just like English can do in instructions:

• Passo il brodo nel colino = I strain the broth through the strainer
• Poi metto la pasta nello scolapasta = Then I put the pasta in the colander

So this is a very normal way to describe a sequence of actions.

Italian usually does not need subject pronouns because the verb ending already shows who is doing the action.

• passo already means I pass / I strain
• metto already means I put

You could say io passo or io metto, but that usually adds emphasis, such as I do it, not someone else. In neutral sentences, Italian normally leaves io out.

Yes, passare often means to pass, but in cooking it can also mean to pass something through a tool, such as a sieve or strainer.

So:

• Passo il brodo nel colino means something like I pass the broth through the strainer
• In natural English, that is usually I strain the broth

This is a good example of how a common verb can have a more specific meaning in a kitchen context.

Nel is a contraction of in + il.

• in + il = nel

In this sentence, nel colino is being used idiomatically with passare to mean something like through the strainer.

Even though nel literally often means in the, here the overall expression is best understood as through the strainer or into the strainer depending on the exact kitchen action.

Italian often uses prepositions a bit differently from English, so it is better to learn this as a natural cooking expression rather than translate word for word.

Because scolapasta is a masculine singular noun beginning with s + consonant (sc-), and that changes the form of the article.

With in, the combined forms are:

• in + il = nel
• in + lo = nello

Since scolapasta takes lo, you get:

• lo scolapasta
• nello scolapasta

Compare:

• nel colino because colino takes il
• nello scolapasta because scolapasta takes lo

A useful basic rule:

Use lo for masculine singular nouns beginning with:

• s + consonant: lo scolapasta
• z: lo zaino
• ps: lo psicologo
• gn: lo gnomo
• x: lo xilofono
• sometimes y

Use il for most other masculine singular nouns:

• il colino
• il brodo

So in your sentence:

• il brodo
• il colino
• lo scolapasta

They are different kitchen tools.

• colino = strainer / small sieve
• scolapasta = colander

A colino is usually finer and smaller, used for filtering liquid or small particles. A scolapasta is usually larger, with holes, used especially for draining pasta.

So the sentence describes two different actions with two different tools:

• first, straining the broth
• then, putting the pasta into the colander

Yes. La pasta can mean pasta in general, and it is very often used with the article in Italian.

Italian uses the definite article much more often than English does. So where English might just say pasta, Italian often says la pasta.

Here, la pasta means the pasta involved in this cooking process, so the definite article sounds natural.

Poi means then / after that / next.

It connects the two actions in sequence:

1. Passo il brodo nel colino
2. poi metto la pasta nello scolapasta

It is very common in instructions, recipes, and spoken explanations.

Yes. If you were giving an instruction directly to someone, you might use the imperative instead of the present indicative.

For example:

• Passa il brodo nel colino, poi metti la pasta nello scolapasta.

That means Strain the broth through the strainer, then put the pasta in the colander.

Your original sentence with passo and metto sounds like someone describing what they do:

• I strain... then I put...

The imperative version sounds like telling you what to do.

Both can work depending on context.

• in the colander focuses on location
• into the colander focuses on movement toward it

Since metto means I put, English often prefers into the colander because there is movement. But in the colander is also possible in natural English.

So:

• Poi metto la pasta nello scolapasta = Then I put the pasta into the colander

is probably the most natural translation.

Yes. They are the direct objects of the two verbs:

• Passo il brodo...
  il brodo is what is being strained
• Metto la pasta...
  la pasta is what is being put somewhere

Then the prepositional phrases tell you where the action happens:

• nel colino
• nello scolapasta

So the structure is:

• verb + direct object + place/tool phrase

It is understandable and fairly natural, especially in informal explanation. But depending on the exact cooking situation, Italians might also say things a little differently.

For example:

• Filtro il brodo con il colino = I filter/strain the broth with the strainer
• Scolo la pasta nello scolapasta = I drain the pasta in the colander

That said, your sentence is useful because it shows everyday verbs and common kitchen vocabulary. A learner should mainly notice:

• passare can mean to strain / pass through
• mettere means to put
• articles and prepositions combine: nel, nello
• kitchen nouns often require specific articles: il colino, lo scolapasta