Demà la reunió començarà a les set.

Putting demà first is a very natural way to set the time frame right away: Tomorrow, the meeting will start at seven.

Catalan word order is fairly flexible here. You could also say:

• La reunió començarà demà a les set.
• La reunió demà començarà a les set. (less neutral)
• A les set començarà la reunió demà. (possible, but less likely in normal conversation)

Starting with demà sounds especially natural when the speaker wants to foreground when it happens.

Because reunió is a countable noun, and Catalan usually uses an article with it when referring to a specific meeting.

• la reunió = the meeting
• una reunió = a meeting

So la reunió tells you both speaker and listener know which meeting is meant. Leaving the article out would normally sound ungrammatical in this sentence.

Yes, reunió is feminine, which is why it takes la:

• la reunió

Many Catalan nouns ending in -ió are feminine, such as:

• la nació
• la informació
• la decisió

So this is a useful pattern to remember, although you should still learn nouns with their article whenever possible.

Començarà is the future tense, third person singular, of començar.

Breakdown:

• infinitive: començar = to begin / to start
• future ending for he/she/it: -à
• començarà = it will begin / it will start

Because the subject is la reunió (the meeting), Catalan uses the third person singular form.

Yes. In everyday Catalan, the present is often used for scheduled future events, just as in English:

• Demà la reunió comença a les set.

That means essentially the same thing as:

• Demà la reunió començarà a les set.

The future form començarà is perfectly correct and a bit more explicitly future. The present comença can sound slightly more immediate or conversational.

Catalan normally uses a before clock times:

• a les dues = at two
• a les cinc = at five
• a les set = at seven

So a here works like English at.

The full phrase means at seven o’clock.

Because Catalan is really treating the time as the seven hours in an old elliptical way. In practice, you just learn the pattern:

• a la una = at one
• a les dues = at two
• a les tres = at three
• a les set = at seven

Notice the exception:

• a la una uses singular la
• all the other usual clock times use plural les

So a les set is simply the normal way to say at seven o’clock.

Because after a les, the hour number by itself is enough:

• a les set = at seven o’clock

You can add more detail if needed:

• a les set del matí = at seven in the morning
• a les set de la tarda = at seven in the afternoon
• a les set del vespre = at seven in the evening

But in many contexts, just a les set is completely normal.

Because Catalan, like English, normally says that a meeting starts rather than is started when you mean the event begins.

So:

• La reunió començarà a les set = The meeting will start at seven

This is the natural active construction. A passive-like idea would usually sound unnatural unless you specifically meant that someone will begin the meeting.

In començarà, the ç is pronounced like an s sound.

So començarà sounds roughly like ko-men-sa-RA.

A few helpful points:

• ç is used before a, o, u to keep the s sound
• without the cedilla, c before a would normally sound like k

So compare:

• començar → s sound
• not comencar → that would suggest a k sound

The final à shows the stress falls on the last syllable: començarà.

They mainly tell you where the stress goes.

• demà → stress on the last syllable
• reunió → stress on the final -ó
• començarà → stress on the final -à

So roughly:

• de-MA
• reu-ni-O
• co-men-sa-RA

The accents are important in writing, not optional decoration.

Yes, often you can. For example:

• Demà la reunió començarà a les set.
• La reunió començarà demà a les set.

Both mean the same basic thing. The difference is emphasis:

• Demà first emphasizes when
• la reunió first emphasizes what event
• a les set first emphasizes the time

Catalan allows this kind of movement more freely than English in many cases, though some orders sound more natural than others depending on context.