Fundurinn er í gangi núna.

Fundurinn is fundur (meeting, masculine) with the definite article attached as a suffix: -inn.

• fundur = a meeting (indefinite)
• fundurinn = the meeting (definite)
  In this sentence, fundurinn is the subject in the nominative case, so you see the nominative definite form.

Er is the present tense of að vera (to be). It links the subject fundurinn to the rest of the information, much like English is:

• Fundurinn er ... = The meeting is ...

Not as a verb tense the way English does. Icelandic doesn’t have a dedicated present continuous form like is running. Instead, it often uses:

• simple present (er) + an expression like í gangi to convey “currently happening / ongoing”.

Yes, núna (now) is flexible. Placing it at the end is very natural. You can also see:

• Fundurinn er núna í gangi.
  Both are understandable; word order changes can shift emphasis slightly, but both are common.

It can be slightly emphatic rather than redundant. Í gangi means in progress, and adding núna highlights right now / at the moment—for example, contrasting with later:

• The meeting is in progress now (so you can’t come in / call / etc.).

You typically put ekki after the verb:

• Fundurinn er ekki í gangi núna. = The meeting isn’t in progress now.

Invert the verb and subject:

• Er fundurinn í gangi núna? = Is the meeting in progress now?

A practical learner-friendly approximation:

• FUND-ur-in er ee GANG-i NOO-na
  Notes:
• Stress is usually on the first syllable: FUNDurinn, GANGi, NÚna.
• í is like a long ee sound.
• The rolled/trilled r and the Icelandic vowel qualities take practice, but the stress pattern helps a lot.

Yes, standa yfir is another common way to say something is ongoing / taking place:

• Fundurinn stendur yfir núna.
  It’s very close in meaning to er í gangi, with a slightly different “feel”: standa yfir is often used for events/periods that are underway, while í gangi is a very general “in progress” phrase. Both are natural for a meeting.