Ceainicul este din porțelan.

Because Romanian usually puts the definite article on the end of the noun.

• ceainic = a teapot / teapot
• ceainicul = the teapot

The ending -ul is the masculine/neuter singular definite article. So instead of a separate word like English the, Romanian attaches it to the noun.

Este is the 3rd person singular of a fi, meaning to be. It corresponds to is.

So:

• Ceainicul este din porțelan. = standard/full form
• Ceainicul e din porțelan. = very common shorter spoken form

Both are correct. Este sounds a bit fuller or more formal, while e is very natural in everyday speech.

Here din means made of or from, depending on context. In this sentence, it shows the material something is made from.

So:

• din porțelan = made of porcelain
• din lemn = made of wood
• din sticlă = made of glass

Even though din often translates as from, with materials it is often best understood as made of.

Because when Romanian names a material in this kind of structure, it normally uses the noun without the definite article.

So you usually say:

• din porțelan
• din lemn
• din metal

not:

• din porțelanul
• din lemnul
• din metalul

The definite form would only appear in a more specific context, such as din porțelanul adus din Franța = from the porcelain brought from France.

This is a very common question, because English can say of porcelain.

In Romanian, when you say what something is physically made from, din is the normal choice:

• Ceainicul este din porțelan.

You will also see de in other structures, especially when the material acts more like a descriptive label attached to a noun:

• o ceașcă de porțelan = a porcelain cup
• o masă de lemn = a wooden table / a table made of wood

So a useful rule is:

• after a fi for material: din is very common
• directly after a noun as a descriptor: de is very common

Ceainic is a neuter noun in Romanian.

Romanian neuter nouns behave:

• like masculine in the singular
• like feminine in the plural

That matters because the definite article and plural forms follow those patterns.

For example:

• singular indefinite: un ceainic
• singular definite: ceainicul
• plural indefinite: două ceainice
• plural definite: ceainicele

In your sentence, it is singular, so it takes the singular definite ending -ul.

This is the normal, neutral word order:

subject + verb + complement

• Ceainicul = subject
• este = verb
• din porțelan = complement

Romanian word order is somewhat flexible, but this version is the most straightforward and natural for a basic statement.

You could change the order for emphasis in special contexts, but learners should treat Ceainicul este din porțelan as the default pattern.

You change the noun form, and in the plural you also change the verb.

• Un ceainic este din porțelan. = A teapot is made of porcelain.
• Ceainicele sunt din porțelan. = The teapots are made of porcelain.

Notice:

• un ceainic = a teapot
• ceainicele = the teapots
• sunt = are

So the original sentence uses the singular definite form: ceainicul = the teapot.