Minulla on tehtävä, johon tarvitsen apua.

Finnish usually expresses possession with olla (to be) plus the possessor in the adessive case.

• Minulla on tehtävä literally means something like At me is a task.
• In normal English, that becomes I have a task.

So where English uses have, Finnish often uses this pattern:

• minulla on = I have
• sinulla on = you have
• hänellä on = he/she has

Minulla is the adessive form of minä (I).

The adessive often has meanings like on, at, or by, but in possession sentences it marks the possessor:

• Minulla on auto. = I have a car.
• Minulla on aikaa. = I have time.

So in this sentence, minulla tells you who has the task.

Because in a normal affirmative possession sentence, the thing possessed is usually in the nominative:

• Minulla on tehtävä.
• Minulla on kirja.

So tehtävä is in its basic dictionary form.

A useful contrast:

• Minulla on tehtävä. = I have a task.
• Minulla ei ole tehtävää. = I do not have a task.

In the negative version, Finnish often changes that noun to the partitive.

Tarvitsen is the 1st person singular present tense of tarvita, which means to need.

So:

• tarvita = to need
• tarvitsen = I need
• tarvitset = you need
• tarvitsee = he/she needs

In this sentence, tarvitsen apua means I need help.

Because Finnish usually does not need a subject pronoun when the verb ending already shows the person.

Here, the ending -n in tarvitsen already tells you the subject is I.

So:

• tarvitsen = I need
• minä tarvitsen = I need, with extra emphasis

Using minä is possible, but it would usually add contrast or emphasis.

Johon is a form of the relative pronoun joka, which can mean who, which, or that.

Here it introduces a relative clause describing tehtävä:

• tehtävä, johon tarvitsen apua
• literally: a task to which I need help
• naturally in English: a task that I need help with

So johon refers back to tehtävä.

Because the relative pronoun takes the case required by its role inside the relative clause.

Here, the idea is roughly I need help for/with that task, so Finnish uses johon, the illative form of joka.

Very roughly:

• johon = into/to which
• jossa = in which
• jota = which/that as a partitive object
• jonka = whose / which as a genitive or total object form

A learner-friendly way to think about it is this:

• English says a task that I need help with
• Finnish uses a case form that matches the structure needed inside the clause
• in this sentence, that form is johon

Apua is the partitive singular of apu (help).

There are two helpful reasons for this here:

1. Tarvita very often takes the partitive.

   • Tarvitsen aikaa. = I need time.
   • Tarvitsen rahaa. = I need money.
   • Tarvitsen apua. = I need help.

2. Help is usually an uncountable or indefinite thing, which also fits the partitive well.

So tarvitsen apua is the normal Finnish way to say I need help.

Because johon tarvitsen apua is a relative clause, and in standard Finnish punctuation, subordinate clauses are separated with a comma.

So the sentence is divided into:

• Minulla on tehtävä = main clause
• johon tarvitsen apua = relative clause describing tehtävä

That is why the comma is there.

Not in standard written Finnish here.

• johon is the correct relative pronoun form, because it refers back to tehtävä
• mihin is usually an interrogative form, meaning to what? or where to?

Compare:

• Mihin tarvitset apua? = What do you need help with?
• tehtävä, johon tarvitsen apua = a task that I need help with

So after a noun like tehtävä, standard Finnish uses johon, not mihin.

Yes. It is a very normal pattern:

1. a possession clause:
   • Minulla on tehtävä
2. followed by a relative clause:
   • johon tarvitsen apua

Finnish often builds longer sentences this way, by putting a relative clause after the noun it describes. So once you understand this example, you can recognize many similar ones:

• Minulla on kirja, jonka ostin eilen.
• Minulla on ystävä, jolle voin puhua.

It is a very useful sentence structure to learn.