Learn Hardcore Finnish: Valaisin putosi pöydältä eilen. - The lamp fell off the table yesterday.

Valaisin is a noun meaning a lamp / light fixture / luminaire (often a bit more “fixture-like” than lamppu, which is a very common everyday word for “lamp”).
It’s in the nominative singular, which is the basic dictionary form and the normal form for the subject of the sentence.

Why is the verb putosi in that form? What is the infinitive?

The infinitive is pudota = to fall.
putosi is past tense (imperfect), 3rd person singular: “(it) fell”.

There’s also a common sound/letter change involved (consonant gradation/alternation in the verb stem):
pudota → puto- → putosi

Could I use a different past form, like a perfect tense?

Yes. Finnish often uses the simple past (imperfect) for completed past events, as here. But you can also say:

Valaisin on pudonnut pöydältä. = “The lamp has fallen from the table.” (perfect; often implies relevance to the present situation)

The given sentence Valaisin putosi pöydältä eilen is the straightforward “It fell yesterday.”

Why is pöydältä not pöytästä or pöydästä?

Because pöydältä is the ablative case, used for movement off a surface:

pöydältä = “from (the top of) the table / off the table”

By contrast:

pöydästä (elative) = “out of the table” (i.e., from inside something—wrong for a normal table surface)

So pöydältä matches the idea of falling off the table.

How do I build pöydältä from pöytä?

It’s pöytä (table) + a stem form + -ltä (ablative ending):

Base noun: pöytä
Stem used here: pöydä- (you’ll see d appear in many case forms)
Case ending: -ltä = “from/off (a surface)”

So: pöydä + ltä → pöydältä

Why is it -ltä and not -lta?

This is vowel harmony.
Because pöytä contains front vowels (ö, ä), Finnish uses the front-vowel version of the ending:

Front-vowel nouns: -ltä
Back-vowel nouns: -lta (e.g., katolta = “off the roof”)

What’s the difference between pöydältä, pöydälle, and pöydällä?

These are the “table surface” location/direction trio:

pöydällä (adessive) = on the table (location)
pöydälle (allative) = onto the table (movement toward)
pöydältä (ablative) = off/from the table (movement away)

So falling off the table naturally uses pöydältä.

Where can eilen go in the sentence? Is the word order flexible?

Yes, Finnish word order is fairly flexible, and moving words often changes focus/emphasis more than basic meaning. All of these are natural:

Valaisin putosi pöydältä eilen.
Eilen valaisin putosi pöydältä. (emphasizes “yesterday”)
Valaisin putosi eilen pöydältä.

The original order is perfectly neutral and common.

Do I need an article like “the” or “a” in Finnish?

No. Finnish has no articles.
Valaisin can mean a lamp or the lamp depending on context. The sentence relies on context (or previous sentences) to make that clear.

How do I pronounce pöydältä and eilen?

A practical guide:

pöy-: like “puh” with rounded lips; öy is a diphthong (similar to German öy, not an English sound)
-dä-: d is usually a soft sound (often like a quick “d” or “th”-like sound depending on speaker)
-ltä: lt is clear; final ä is like the a in “cat” but more fronted

eilen is roughly AY-len (two syllables), with the stress on the first syllable: EI-len.

Could the sentence omit the subject, like “Fell off the table yesterday”?

Not in standard Finnish. Finnish can drop pronouns (because verb endings show person), but here the subject is a noun (valaisin), so you normally keep it:

Valaisin putosi... (normal)

You could omit it only if it’s clearly understood from context and you’re using a different structure, but the straightforward sentence needs the subject.

Is valaisin the best word here, or would Finns say something else?

Both are possible, but they feel slightly different:

Valaisin: a bit more formal/technical, can suggest a light fixture (e.g., desk lamp, ceiling light unit, etc.)
Lamppu: very common everyday word for lamp

So Lamppu putosi pöydältä eilen is also perfectly natural if you mean a regular lamp.