Ovaj muškarac je lončar.

Because ovaj has to agree with muškarac in gender, number, and case. Muškarac is masculine singular nominative, so the correct demonstrative is ovaj.

Compare:

• ovaj muškarac = this man
• ova žena = this woman
• ovo dijete = this child

Not exactly.

• muškarac specifically means an adult male / a man
• čovjek can mean human being, person, or sometimes man, depending on context

In this sentence, muškarac is the more precise word if you want to identify someone as male.

Je is the 3rd person singular present of biti, the verb to be. In this sentence, it means is.

So:

• ja sam = I am
• ti si = you are
• on/ona/ono je = he/she/it is

In standard Croatian, no. You normally need je in an ordinary present-tense sentence like this.

So the standard form is:

• Ovaj muškarac je lončar.

Leaving out je would sound nonstandard, poetic, or like a headline rather than a normal full sentence.

After biti, Croatian normally uses the nominative for a predicate noun, especially when you are saying what someone is by identity, profession, or category.

So you get:

• On je učitelj.
• Ona je liječnica.
• Ovaj muškarac je lončar.

That is why lončar stays in its basic dictionary form.

Croatian does not have articles. There is no separate word that directly matches English a or the.

Instead, Croatian uses:

• context
• word order
• demonstratives like ovaj, taj, onaj

So ovaj muškarac already gives the idea of this man, and no article is needed.

Yes, but different word orders create different emphasis.

The most neutral version is:

• Ovaj muškarac je lončar.

You may also hear:

• Ovaj je muškarac lončar.

Because je is a clitic, it usually appears very early in the sentence, often after the first phrase or stressed element. Other word orders are possible, but they can sound more emphatic or marked.

The standard yes/no question is:

• Je li ovaj muškarac lončar?

In everyday speech, you will also hear:

• Je l' ovaj muškarac lončar?

That is the usual way to turn this kind of sentence into a question in Croatian.

Yes. You can say:

• Muškarac je lončar.

That is grammatical, but it no longer means this man specifically. Without ovaj, the exact English translation depends more on context, for example the man is a potter or a man is a potter.

Roughly:

• ovaj = /ɔvaj/
• muškarac = /muʃkarats/
• je = /je/
• lončar = /lɔntʃar/

Useful letter sounds:

• j = y as in yes
• š = sh
• č = ch
• c = ts

So an approximate pronunciation is:

• OH-vai moo-SHKA-rats yeh LON-char

A natural feminine version would be:

• Ova žena je lončarka.

Here:

• ova matches the feminine noun žena
• lončarka is the feminine form of lončar

These are all demonstratives, but they point to different things:

• ovaj = this, near the speaker
• taj = that, often near the listener or already mentioned
• onaj = that over there, farther away

So if you change ovaj to taj or onaj, the grammar stays similar, but the sense of distance changes.