Learn Icelandic: Þetta er mikilvægur atburður.

When you introduce something using 'This is...' or 'That is...', Icelandic always uses the neuter singular form þetta (this) regardless of the noun's gender. The adjective mikilvægur still has to match the masculine gender of atburður, but the introductory 'this' stays neutral.

How can I tell that atburður is a masculine noun?

The -ur ending is a very strong clue that atburður is a masculine noun. You can also clearly see the gender from the adjective mikilvægur, which takes the masculine nominative ending -ur to match the noun it describes.

What is the literal meaning behind the adjective mikilvægur?

It comes from mikill (great or much) and vægi (weight). So something that is mikilvægur literally 'carries a lot of weight'. Breaking down long Icelandic words like this makes them much easier to remember at this level!

Since this lesson is about time and events, how would I talk about multiple events and say 'These are important events'?

You would say Þetta eru mikilvægir atburðir. Notice that the introductory Þetta stays exactly the same for plural 'these', but the verb (eru), the adjective (mikilvægir), and the noun (atburðir) all change to their plural forms.