Learn Hardcore Finnish: Taskulampun valo auttaa minua löytämään polun hämärässä metsässä. - The light of the flashlight helps me find the path in the dim forest.

valo is in the nominative case and is the thing that performs the action: the light helps.
taskulampun is in the genitive case and modifies valo, showing whose light it is.

So taskulampun valo literally means the flashlight’s light / the light of the flashlight, and that whole noun phrase is the subject of the sentence, with valo as its head and taskulampun as a possessor/attribute.

Why is taskulampun in the genitive case?

Finnish uses the genitive case very often to show possession or a similar relationship.

taskulamppu = flashlight (basic dictionary form, nominative)
taskulampun = of the flashlight (genitive)

Here, taskulampun tells us whose light it is: taskulampun valo = the light of the flashlight.

This is the normal, neutral way to say the light of X in Finnish:

auringon valo = the sun’s light
kynttilän liekki = the candle’s flame
taskulampun valo = the flashlight’s light

Why does taskulamppu become taskulampun (one p instead of pp)?

This is an example of Finnish consonant gradation.

Nominative: taskulamppu (double pp)
Genitive: taskulampun (single p)

In many words, a strong grade consonant (like pp, kk, tt) appears in one form, and a weak grade (p, k, t) appears in another, depending on the syllable structure and case.

Here, pp → p when we go from the nominative taskulamppu to the genitive taskulampun.

You see the same type of change in other words, for example:

kappa → kapan
kauppa → kaupan

Why is it minua and not minut after auttaa?

Minua is the partitive form of minä (I, me), and minut is the accusative form.

With the verb auttaa (to help), the normal object form is the partitive:

auttaa minua = to help me
auttaa sinua = to help you
auttaa häntä = to help him/her

So auttaa minua is the standard pattern: auttaa + partitive object.

There is also a structure with the total/accusative object (minut), but it is used in a more result-focused way and almost always with some complement that shows what you are being helped to become or to achieve, for example:

Hän auttoi minut ylös. = He helped me up.
He auttoivat minut turvaan. = They helped me to safety.

In your sentence, we are simply saying that the light helps me (in the process) to find the path, so the normal, ongoing, non-result-marking object form minua is used.

What exactly is löytämään, and why not just use löytää?

Löytämään is the third infinitive in the illative case (often called the ‑maan / ‑mään form).

Base verb: löytää = to find

Third infinitive (illative): löytämään

This form is commonly used after verbs like:

auttaa (to help)
opettaa (to teach)
ryhtyä (to start, to begin to)
jäädä (to stay to do something)

The pattern is:

auttaa + partitive object + verb in ‑maan/‑mään

So:

auttaa minua löytämään = to help me (in) finding / to help me find
auttaa lapsia lukemaan = to help the children read

Using löytää (the basic infinitive) here would not be standard; the natural Finnish construction after auttaa is with the ‑maan/‑mään infinitive: auttaa tekemään jotakin (help to do something).

Why is polun in the genitive case, not polku or polkua?

Polun is the genitive singular of polku (path).

In Finnish, the object of a verb can be:

in the genitive (often called a total object), or
in the partitive (often called a partial object), among other patterns.

Here, polun is the object of the infinitive löytämään, and the genitive signals a total object: the idea is that you find the whole, specific path.

So:

löytämään polun ≈ to find the path (completely, as a whole, a particular path)

If we used nominative polku, that would be ungrammatical here — nominative is not used as the object form in this structure.

If we used partitive polkua, the meaning would change slightly (see the next question).

What is the difference in meaning between polun and polkua here?

Both polun and polkua are possible after löytämään, but they express different nuances:

löytämään polun
- polun = genitive = total object
- Implies finding a specific, complete path.
- The action is seen as having a clear end point: you get the path located.
löytämään polkua
- polkua = partitive = partial or indefinite object
- Can suggest:
  - looking for some path, any path, not a specific one, or
  - being in the process of finding a path (ongoing, not necessarily completed).

In your sentence, polun makes it feel like there is some particular path you want to locate, and the light helps you successfully find it.

Why are both hämärässä and metsässä in the inessive (‑ssa) case?

In Finnish, adjectives generally agree with the nouns they modify in:

case
number
(and often) sometimes other features

Here:

metsässä = in a forest (inessive singular of metsä)
hämärä = dim, dusky (adjective)
hämärässä = inessive singular form of hämärä

Because hämärä modifies metsä, it takes the same case and number:

nominative: hämärä metsä = a dim forest
inessive: hämärässä metsässä = in a dim forest

You cannot say hämärä metsässä with only the noun inflected; that would be ungrammatical in standard Finnish. Both the adjective and the noun must match: hämärässä metsässä.

How would the meaning change if we used metsään or metsästä instead of metsässä?

The three forms are different local cases with different basic meanings:

metsässä (inessive) = in the forest
metsään (illative) = into the forest
metsästä (elative) = out of / from the forest

In your sentence:

hämärässä metsässä = in a dim forest

If you said:

hämärään metsään = into a dim forest
- The emphasis moves to motion into the forest (for example: the light helps you find a path into the dim forest).
hämärästä metsästä = from a dim forest
- That would describe something like finding a path out from a dim forest.

So metsässä is correct here because the situation is located inside the forest, not moving into or out of it.

Can the word order be changed, for example to Minua auttaa taskulampun valo löytämään polun hämärässä metsässä?

Finnish word order is quite flexible, and changing it usually affects emphasis rather than basic grammar.

Your original order is neutral:

Taskulampun valo auttaa minua löytämään polun hämärässä metsässä.
- Focus is on the fact that the flashlight’s light helps you.

If you say:

Minua auttaa taskulampun valo löytämään polun hämärässä metsässä.

This is still grammatical, but it slightly shifts the emphasis:

minua is now in the first position, so there is a bit more focus on me (for example, in contrast to someone else: me, not you).
taskulampun valo then comes later as the thing that does the helping.

You could also bring the place to the front for emphasis:

Hämärässä metsässä taskulampun valo auttaa minua löytämään polun.
- Emphasizes the setting: In a dim forest, the flashlight’s light helps me…

So yes, you can change the word order, but the original version is the most neutral, straightforward one.