Metti la pentola sul sottopentola, altrimenti il tavolo si rovina.

Here metti is a command: the informal singular imperative, used when speaking to tu.

So:

• mettere = to put
• tu metti = you put
• metti! = put!

This is very common in Italian: for many verbs, the tu imperative has the same form as the present indicative.

So Metti la pentola... means Put the pot..., not You put the pot... in this context.

Italian uses definite articles much more regularly than English. In this sentence:

• la pentola = the pot
• il tavolo = the table
• il sottopentola = the trivet / pot stand

Even if English might sometimes sound natural with less emphasis on the article, Italian normally keeps it.

Here the objects are understood as specific, visible, or relevant in the situation: the pot, the table, the trivet.

Sul means on the.

It is a contraction of:

• su = on
• il = the

So:

• su + il = sul

Examples:

• sul tavolo = on the table
• sul libro = on the book
• sul sottopentola = on the trivet

This is one of the standard Italian preposition + article combinations.

Good question. Even though sottopentola ends in -a, it is normally masculine: il sottopentola.

That is why the sentence has:

• su + il = sul sottopentola

and not:

• su + la = sulla sottopentola

Italian gender is not always predictable just from the ending, especially with compound words like sottopentola.

Sottopentola is a noun meaning trivet, pot stand, or something you put a hot pot on to protect the table.

It is a compound word built from:

• sotto = under
• pentola = pot

So the idea is literally something under the pot.

This kind of compound word is very common in Italian.

Because the idea is that the pot is being placed on top of a surface.

• su = on
• in = in / inside
• a usually does not work for this meaning

So:

• Metti la pentola sul sottopentola = Put the pot on the trivet

You are not putting the pot inside something, but onto it.

Yes, sopra il sottopentola is understandable, but sul sottopentola is more natural here.

Both can mean on the trivet, but:

• sul is the normal compact way to express physical placement on a surface
• sopra can sound a bit more spatial or emphatic, like above/on top of

So in an everyday instruction, Metti la pentola sul sottopentola is the most idiomatic choice.

Altrimenti means otherwise.

It introduces the consequence if the listener does not do what was just said:

• Metti la pentola sul sottopentola, altrimenti il tavolo si rovina.
• Put the pot on the trivet, otherwise the table gets damaged.

It links the command and the warning very naturally.

Because rovinarsi is often used to mean to get damaged, to get ruined, or to become spoiled.

Compare:

• rovinare qualcosa = to damage something
  
  • Il calore rovina il tavolo. = The heat damages the table.
• rovinarsi = to get damaged / to get ruined
  
  • Il tavolo si rovina. = The table gets damaged.

So in this sentence, si does not mean the table is doing something to itself on purpose. It is part of a very common Italian way of expressing that something undergoes damage.

Yes. In Italian, si is very often used with inanimate things when the meaning is gets + adjective/past participle idea or undergoes a change.

Examples:

• Il pane si secca. = The bread gets dry.
• La maglia si restringe. = The sweater shrinks.
• Il tavolo si rovina. = The table gets damaged.

So this is completely normal Italian.

Italian often uses the present tense to express a likely or general consequence, especially in everyday speech.

So:

• altrimenti il tavolo si rovina literally looks like otherwise the table gets damaged

but in context it means:

• otherwise the table will get damaged
• otherwise you’ll ruin the table

Using the present makes the warning sound immediate and natural.

You could say si rovinerà, but si rovina is very common and idiomatic here.

Not exactly.

• il tavolo si rovina = the table gets damaged
• rovini il tavolo = you damage the table / you’ll damage the table

The sentence with si rovina focuses on what happens to the table. The version with rovini focuses more directly on you as the person causing the damage.

Both are possible in real life, but the original sentence sounds a bit less accusatory and more like a practical warning.

Yes, that is also possible.

Both of these work:

• Altrimenti il tavolo si rovina.
• Altrimenti si rovina il tavolo.

The first is more neutral and straightforward. The second can sound a little more spoken or emphatic, with the result coming first.

Italian word order is often more flexible than English, especially in everyday speech.

You would usually say:

• Mettila sul sottopentola.

That is:

• metti = put
• la = it (referring to la pentola)
• mettila = put it

Because pentola is feminine, the direct object pronoun is la.

So:

• Metti la pentola sul sottopentola. becomes
• Mettila sul sottopentola.

It is addressed to one person informally, because of metti.

If you were speaking to:

• one person formally: Metta la pentola sul sottopentola...
• more than one person: Mettete la pentola sul sottopentola...

So metti clearly signals tu.

Yes, if the object changes, the sentence structure stays the same.

For example:

• Metti la padella sul sottopentola. = Put the pan on the trivet.
• Metti il tegame sul sottopentola. = Put the casserole pot / baking dish on the trivet.

But if the noun changes gender, other words may change too:

• la padella → still feminine
• il tegame → masculine

The structure Metti + noun + sul sottopentola stays the same.