Jag tackar min vän för hjälpen.

A simple breakdown is:

• Jag = the subject
• tackar = the verb
• min vän = the direct object, the person being thanked
• för hjälpen = a prepositional phrase telling you what the thanks is for

So the structure is basically:

subject + verb + object + for-phrase

That is a very normal Swedish sentence pattern.

Because tackar is the finite present-tense form, and Swedish main clauses need a finite verb.

• infinitive: tacka
• present tense: tackar

So:

• att tacka = to thank
• jag tackar = I thank / I am thanking

Swedish usually forms the present tense by adding -r to the infinitive, so tacka → tackar.

Yes, it is grammatical and natural, but it can sound somewhat formal, deliberate, or written depending on context.

In English, I thank my friend for the help sounds formal. Swedish Jag tackar min vän för hjälpen can have a similar feel.

In everyday speech, people might also say things like:

• Jag vill tacka min vän för hjälpen = I would like to thank my friend for the help
• Tack för hjälpen! = Thanks for the help!

So your sentence is correct, but the tone may be a little more formal than casual everyday conversation.

Because Swedish uses the pattern:

tacka någon för något
= to thank someone for something

So:

• tacka min vän = thank my friend
• för hjälpen = for the help

This is just the normal verb pattern that goes with tacka.

Swedish possessives change depending on the noun.

• min is used with singular en-words
• mitt is used with singular ett-words
• mina is used with plurals

Since vän is an en-word and singular, you use min:

• en vän
• min vän

Compare:

• mitt hus = my house
• mina vänner = my friends

Because the possessive already determines the noun.

In English, you also say my friend, not the my friend or a my friend. Swedish works similarly:

• min vän = my friend

So you do not add en here.

In Swedish, when a noun has a possessive before it, the noun is normally in its basic singular or plural form, not the definite form.

So:

• vännen = the friend
• min vän = my friend

You do not usually combine a possessive like min with the definite ending -en on the noun.

That is why min vän is correct, while min vännen is not.

Because hjälpen refers to specific help, the help that was given.

• hjälp = help, in a general sense
• hjälpen = the help, a specific instance of help

In this sentence, the speaker is thanking the friend for a particular help already received, so the definite form sounds natural:

• för hjälpen = for the help

In fact, Tack för hjälpen is a very common Swedish expression.

They follow different grammar rules.

• min vän is not definite in form because the possessive min already makes it definite in meaning
• hjälpen has no possessive in front of it, so Swedish marks definiteness directly on the noun with -en

So:

• min vän = possessive determiner + basic noun form
• hjälpen = noun with definite ending

This difference is completely normal in Swedish.

Vän is an en-word.

That is why you get:

• en vän
• vännen
• min vän

If it were an ett-word, the possessive would be mitt instead of min.

The sentence uses normal main-clause word order:

Jag + tackar + min vän + för hjälpen

That is:

• subject
• verb
• object
• prepositional phrase

This is the most neutral way to say it.

Swedish does also have the V2 rule, so if you move another element to the front, the verb still stays in second position. For example:

• Min vän tackar jag för hjälpen is possible in a marked or poetic context, but not the normal neutral version
• För hjälpen tackar jag min vän is also possible but sounds more formal or stylistically marked

For ordinary use, Jag tackar min vän för hjälpen is the standard order.