A futár fenntartja a kapcsolatot.

A is the Hungarian singular definite article, usually equivalent to the in English.

So:

• a futár = the courier
• a kapcsolatot = the contact / the connection / the relationship as the object

Hungarian uses the definite article very regularly. Also, a changes to az before a vowel sound, but here both words begin with consonants, so a is correct.

Futár means courier.

It has no special ending here because it is the subject of the sentence, and Hungarian subjects are usually in the nominative case, which normally has no ending.

So:

• futár = courier
• a futár = the courier

Unlike the object, the subject is unmarked.

Fenntartja means maintains, keeps up, or in some contexts keeps in contact / maintains the connection.

It comes from the verb fenntart = to maintain.

So the sentence structure is roughly:

• A futár = the courier
• fenntartja = maintains
• a kapcsolatot = the contact / connection

Because Hungarian verbs change depending on whether they take a definite object.

Here the object is a kapcsolatot = the contact/connection, which is definite, so Hungarian uses the definite conjugation.

• fenntart = he/she maintains something indefinite, or no object stated
• fenntartja = he/she maintains it / the specific thing

So fenntartja is used because the sentence has a definite object.

Because kapcsolatot is the direct object of the sentence, and Hungarian marks direct objects with the accusative ending.

The base word is:

• kapcsolat = contact, connection, relationship

As an object, it becomes:

• kapcsolatot

The core accusative marker is -t, but Hungarian often inserts a linking vowel, so here you get -ot.

So:

• kapcsolat = connection
• kapcsolatot = connection as the thing being maintained

Kapcsolat is a flexible word. Depending on context, it can mean:

• contact
• connection
• relationship
• communication link

In the phrase fenntartja a kapcsolatot, it often means something like:

• maintains contact
• keeps the connection going
• stays in touch
• maintains the relationship

The best English translation depends on the situation.

Yes. Fenntartani a kapcsolatot is a very natural Hungarian expression.

It is commonly used for:

• keeping in touch with someone
• maintaining a working relationship
• maintaining communication
• keeping some kind of connection active

So this is not just a word-for-word combination; it is a normal phrase Hungarian speakers really use.

No, Hungarian word order is fairly flexible, but changing it changes the focus or emphasis.

This version is a fairly neutral one:

• A futár fenntartja a kapcsolatot.

It presents a futár as the topic, then says what the courier does.

Other word orders are possible, for example:

• A kapcsolatot a futár fenntartja.

That would put more emphasis on the connection/contact.

Because Hungarian marks the object with -t, the roles are still clear even when the order changes.

Then the verb would usually switch to the indefinite conjugation.

For example:

• A futár fenntart egy kapcsolatot.

Here:

• egy kapcsolatot = a connection / a contact (indefinite)
• the verb is fenntart, not fenntartja

So the contrast is:

• fenntartja a kapcsolatot = maintains the connection
• fenntart egy kapcsolatot = maintains a connection

A few useful pronunciation points:

• Hungarian stress is usually on the first syllable of each word.
• futár is stressed on fu-
• fenntartja is stressed on fenn-
• kapcsolatot is stressed on kap-

Also:

• á is a long vowel
• the double consonant in fenn- is pronounced longer than a single n

A rough English-style approximation might be:

• uh FOO-taar fenn-TAR-tyaw uh KOP-cho-law-tot

That is only approximate, but the main thing to remember is: stress the first syllable of each Hungarian word.