Learn Hardcore Icelandic: Fundurinn hefst klukkan níu. - The meeting starts at nine o’clock.

Fundur means meeting. Icelandic usually adds the definite article to the end of the noun, so fundurinn means the meeting. The ending -inn is the suffixed definite article. In this sentence, fundurinn is the subject.

What form is hefst?

Hefst is the 3rd person singular present tense of hefjast, which means to begin or to start. It matches the singular subject fundurinn. So grammatically it is the same kind of form as English starts.

Is hefst passive because it ends in -st?

Not in this sentence. The -st ending often belongs to what is called the middle voice in Icelandic. Sometimes that overlaps with passive or reflexive meanings, but here you should simply learn hefjast as a verb meaning begin / start. So hefst here just means begins / starts.

Why is the present tense used if the meeting happens in the future?

Because Icelandic, like English, often uses the present tense for scheduled future events. English says The meeting starts at nine, and Icelandic does the same thing with Fundurinn hefst klukkan níu. It does not mean the meeting is starting right now.