Metto la tazza sulla tovaglietta.

Because Italian usually drops the subject pronoun when it is clear from the verb ending.

• metto already means I put / I am putting
• the -o ending tells you the subject is I

So io metto is possible, but it is normally used only for emphasis, contrast, or clarity:

• Io metto la tazza, tu metti il piatto.
  I put the cup down, you put the plate down.

In a neutral sentence, Metto la tazza sulla tovaglietta is the most natural choice.

Metto is the present indicative of mettere.

In English, the Italian present tense can often translate in more than one way depending on context:

• I put the cup on the placemat
• I am putting the cup on the placemat
• sometimes even I do put the cup on the placemat

Italian does not always separate simple present and present continuous the way English does.

Because it is the 1st person singular form of the verb mettere.

Here is the present tense:

• io metto = I put
• tu metti = you put
• lui/lei mette = he/she puts
• noi mettiamo = we put
• voi mettete = you all put
• loro mettono = they put

So the -o ending is one of the clues that the hidden subject is io.

In Italian, you usually need an article before a noun in cases like this.

So:

• la tazza = the cup

Leaving out the article would usually sound incomplete or unnatural here.

Italian uses articles more often than English. English can sometimes omit them in places where Italian normally does not.

Because la and una do different jobs:

• la tazza = the cup, a specific cup
• una tazza = a cup, any cup / one cup not yet identified

So the sentence with la tazza suggests that the cup is already known from the situation or context.

Because sulla is the normal contracted form of:

• su
  • la = sulla

Italian commonly combines simple prepositions with definite articles:

• su + il = sul
• su + lo = sullo
• su + la = sulla
• su + i = sui
• su + gli = sugli
• su + le = sulle

So sulla tovaglietta means on the placemat.

Because sulla already includes the article:

• su = on
• la = the
• sulla = on the

So the sentence is not just saying on placemat; it is saying on the placemat.

That article is normally required here in Italian.

Yes, you often could say sopra la tovaglietta, but there is a small difference in feel.

• su often means on, with the idea of being placed on a surface
• sopra means above / on top of, and can sound a little more spatial or emphatic

In many everyday situations, both are possible:

• sulla tovaglietta
• sopra la tovaglietta

But sulla tovaglietta is very natural for simply saying where you place something.

Tovaglietta is a noun formed from tovaglia.

• tovaglia = tablecloth
• tovaglietta = little tablecloth / placemat

The ending -etta is a diminutive ending. It often gives the idea of something smaller or sometimes just a slightly different everyday version of the base noun.

So tovaglietta is the natural word for a placemat.

Because this is the normal Italian order:

• verb
  • direct object
    • place/location phrase

So:

• Metto = I put
• la tazza = the cup
• sulla tovaglietta = on the placemat

This is the most neutral, standard order.

Italian can change word order for emphasis, but this version is the plain, natural one.

Yes. That is possible, but it changes the emphasis.

• Metto la tazza sulla tovaglietta = neutral
• La tazza la metto sulla tovaglietta = emphasizes the cup

That second version uses dislocation and a resumptive pronoun (la), which is common in spoken Italian when highlighting the object.

It can sound like:

• The cup, I put it on the placemat.

It is partly irregular, or at least not completely straightforward.

It belongs to the -ere group, but some forms are not fully predictable if you only know the infinitive. For example:

• mettere
• metto
• metti
• mette
• mettono

It is a very common verb, so it is worth memorizing well.

Yes. Very often, yes.

The Italian present tense can cover both:

• a simple present meaning
• an action happening right now

If you want to be especially explicit about an action in progress, Italian can also use:

• Sto mettendo la tazza sulla tovaglietta.

But in many ordinary situations, Metto la tazza sulla tovaglietta works perfectly well.

The double tt matters in Italian pronunciation.

metto is pronounced with a held/doubled consonant, not like a single light t. The double consonant is part of the spelling and pronunciation of the verb form.

So learners should notice:

• meto would be wrong
• metto is correct

In Italian, double consonants are important and can change meaning.

Yes. Mettere is a very common verb with many uses.

Besides physical placement, it can also mean things like:

• to put on clothes
• to place
• to set
• to insert
• to cause someone to be in a state, in some expressions

But in this sentence, it is the straightforward physical meaning: placing something somewhere.