Keraamikko auttaa aloittelijaa savityöpajassa.

Because aloittelijaa is the partitive singular form of aloittelija.

In this sentence, the verb auttaa normally takes its object in the partitive:

• auttaa jotakuta = to help someone

So:

• aloittelija = a beginner
• aloittelijaa = a beginner / the beginner, as a partitive object

This is something you usually just learn with the verb:

• autan ystävää = I help a friend / my friend
• hän auttaa aloittelijaa = he/she helps a beginner

Here, the partitive is mainly due to the verb’s grammar, not because the help is somehow incomplete.

Savityöpajassa is in the inessive case, which usually means in or inside.

So:

• savityöpaja = clay workshop / pottery workshop
• savityöpajassa = in the clay workshop

The ending -ssa / -ssä is very common:

• talossa = in the house
• kaupungissa = in the city
• pajassa = in the workshop

Because savityöpaja has back vowels, it takes -ssa, not -ssä.

Keraamikko is in the nominative singular, which is the basic dictionary form of the noun.

Here it is the subject of the sentence:

• Keraamikko auttaa aloittelijaa.
• The ceramic artist / potter helps the beginner.

In Finnish, the subject is often in the nominative when the sentence is a normal active sentence like this one.

Because in Finnish, the 3rd person singular present tense of many verbs looks the same as the basic infinitive form.

For auttaa:

• auttaa = to help
• hän auttaa = he/she helps

Other forms make this clearer:

• autan = I help
• autat = you help
• auttaa = he/she helps
• autamme = we help
• autatte = you all help
• auttavat = they help

So in your sentence, auttaa means helps, not to help, because the sentence structure shows it is a finite verb.

Finnish does not normally use articles like English a, an, or the.

So:

• keraamikko can mean a ceramic artist or the ceramic artist
• aloittelijaa can mean a beginner or the beginner

Context tells you which meaning is most natural.

That means the sentence could be understood as something like:

• A ceramic artist helps a beginner in a clay workshop
• The ceramic artist helps the beginner in the clay workshop

English has to choose; Finnish often does not.

Yes. Finnish uses compound words very often.

Savityöpaja is made of:

• savi = clay
• työpaja = workshop

Together:

• savityöpaja = clay workshop / pottery workshop

A useful rule is that the last part is the main word. Here the main word is työpaja (workshop), and savi tells you what kind of workshop it is.

Also, when a compound gets a case ending, the ending goes on the whole compound:

• savityöpaja
• savityöpajassa

Yes. Finnish word order is more flexible than English word order because the case endings show what each word is doing.

The neutral order here is:

• Keraamikko auttaa aloittelijaa savityöpajassa.

But you could also say:

• Savityöpajassa keraamikko auttaa aloittelijaa.
  This emphasizes the location: In the clay workshop, the ceramic artist helps the beginner.

You might also hear other orders in context, especially in speech or for emphasis. The meaning stays mostly clear because:

• keraamikko is the subject
• aloittelijaa is marked as the object
• savityöpajassa is marked as a location

So Finnish does not rely on word order as heavily as English does.

Here, aloittelijaa is partitive singular.

That can be confusing, because some Finnish endings can look similar at first. But the basic form is:

• aloittelija = beginner
• aloittelijaa = beginner, in the partitive singular

The plural partitive would be different:

• aloittelijoita = beginners

So:

• Keraamikko auttaa aloittelijaa. = The ceramic artist helps a beginner / the beginner.
• Keraamikko auttaa aloittelijoita. = The ceramic artist helps beginners.

Yes, that is a good way to think about it.

Aloittelija comes from the verb aloittaa, which means to begin or to start. The noun aloittelija means beginner or someone who is just starting out.

This -ja / -jä ending is common in nouns referring to a person connected with an action:

• opettaa = to teach → opettaja = teacher
• kirjoittaa = to write → kirjoittaja = writer
• aloittaa = to begin → aloittelija = beginner

Then in this sentence it becomes partitive:

• aloittelija → aloittelijaa

A few helpful pronunciation points:

• Finnish stress usually falls on the first syllable of each word.
• Double letters matter: they are pronounced longer.
• Finnish spelling is very regular, so you usually pronounce what you see.

Roughly:

• KE-raa-mik-ko
• AUT-taa
• A-loit-te-li-jaa
• SA-vi-TYÖ-pa-jas-sa

A few details:

• aa in auttaa and aloittelijaa is a long vowel.
• tt in auttaa is a long consonant.
• työ contains the vowel combination yö, which may take practice for English speakers.
• j in Finnish is pronounced like English y in yes.

So aloittelijaa is pronounced more like a-loit-te-li-yaa, not with an English j sound.