Learn Hardcore Swedish: Han blir osäker när mötet börjar. - He becomes uncertain when the meeting starts.

Han är osäker när mötet börjar = He is insecure when the meeting starts (describes a general, ongoing state).
Han blir osäker när mötet börjar = He becomes / gets insecure when the meeting starts (focuses on the change that happens at that moment).

Swedish often uses bli with feelings and states that are triggered by something:

Hon blir nervös när hon pratar inför folk.
Vi blir trötta på kvällen.

So blir is natural here because his insecurity appears when the meeting starts, not all the time.

What exactly does osäker mean here? Is it “insecure” about himself or “uncertain” about something?

Osäker covers both ideas in Swedish:

Insecure / lacking confidence (about oneself)
- Han är osäker på sig själv. – He is insecure about himself.
Uncertain / unsure (about facts or decisions)
- Jag är osäker på svaret. – I’m unsure of the answer.

In Han blir osäker när mötet börjar, context decides which nuance is meant.
Most naturally, it suggests he feels nervous or lacks confidence when the meeting starts, but it could also mean he becomes unsure what to say or do.

Why is it mötet and not just möte?

Möte is a neuter noun:

ett möte = a meeting (indefinite singular)
mötet = the meeting (definite singular)

In this sentence, it is a specific meeting that both speaker and listener know about, so Swedish uses the definite form mötet.

Compare:

Han blir osäker när mötet börjar.
He gets insecure when the meeting starts. (that particular meeting)
Han blir osäker när ett möte börjar.
He gets insecure when a meeting starts. (any meeting; more general, less common way to express this idea)

How do I know that möte takes -et in the definite form and not -en?

Swedish nouns are divided into two grammatical genders:

en-words (common gender): en stol, stolen (chair, the chair)
ett-words (neuter): ett möte, mötet (meeting, the meeting)

Möte is an ett-word, so its definite singular ending is -et → mötet.

Unfortunately, the gender is not always predictable from the form of the noun.
In practice, you learn each new noun together with en or ett, for example:

ett möte – mötet
ett hus – huset
en bok – boken

Why is the word order när mötet börjar and not när börjar mötet?

This is because när mötet börjar is a subordinate clause (introduced by när).

In Swedish:

In a main clause, the verb is usually in second position (V2):
- Mötet börjar nu.
- Nu börjar mötet.
In a subordinate clause, the finite verb normally comes after the subject:
- … när mötet börjar.
- … eftersom mötet börjar.

So in Han blir osäker när mötet börjar, mötet is the subject and börjar is the verb, in the normal subordinate-clause order.

När börjar mötet? is also possible, but that is a main clause (a question: When does the meeting start?), not the same structure as in your example.

Can I put the när-clause first, like När mötet börjar blir han osäker?

Yes, that is perfectly correct:

När mötet börjar blir han osäker.
Han blir osäker när mötet börjar.

Both are natural. When the när-clause comes first, many writers do not use a comma if the sentence is short:

När mötet börjar blir han osäker.

A comma (När mötet börjar, blir han osäker.) is not wrong, but in modern Swedish it is often omitted in simple sentences like this.

Could I say Han blir osäker om mötet börjar instead of när mötet börjar?

Normally, no. Om and när are not interchangeable here.

när = when (talking about actual time)
- Han blir osäker när mötet börjar.
  He gets insecure when the meeting starts. (and we assume it really starts)
om = if (talking about a condition)
- Han blir osäker om mötet börjar.
  This would mean something like He gets insecure *if the meeting starts,
  as if there is a real possibility that the meeting *might not start.

In a normal situation, the meeting is scheduled and will start, so Swedish uses när, not om.

Why don’t we say när att mötet börjar? In English we might say “when that the meeting starts” (even if it sounds odd).

Swedish does not stack conjunctions like that. You use either:

att (that)
Jag vet att mötet börjar klockan tre.
I know that the meeting starts at three.

a time/condition word like när, innan, om
Han blir osäker när mötet börjar.

You cannot combine them here:

❌ när att mötet börjar – ungrammatical
✅ när mötet börjar

So när alone is enough to introduce the clause.

Is there a difference between börjar and startar in this context?

Both börjar and startar can translate as starts, but their usage is a bit different:

börja is the more neutral and common verb for activities, events, and processes:
- Mötet börjar klockan två.
- Filmen börjar snart.
starta is common with machines, technical things, and also in some everyday uses:
- Bilen startar inte.
- Vi startar projektet nästa vecka.

In the sentence:

Han blir osäker när mötet börjar.
This is the most natural phrasing.

You can say när mötet startar, but it sounds a bit more technical or formal; börjar is the default for a meeting.

How do you pronounce Han blir osäker när mötet börjar?

Approximate pronunciation (Swedish standard) in syllables:

Han – like hahn (short a, open, not like English han in hand)
blir – bliir, long i (like English ee in see), final r is often light
osäker – OO-sä-ker
- o like English oo in food
- sä with ä like e in bed, but a bit more open and long
- ker with a clear k and er similar to air but shorter
när – när, with long ä (similar to air but not a diphthong)
mötet – MÖÖ-tet
- mö with ö (no exact English equivalent; like saying e in her with rounded lips)
- first syllable mö is long, -tet is short
börjar – roughly BÖR-jar
- bör with the same ö sound
- jar with Swedish j like English y in yes → yar

Main stress falls on osä- in osäker and mö- in mötet:

Han blir OSÄker när MÖtet BÖRjar.