Learn Swedish: Du måste ta den här möjligheten! - You must take this opportunity!

The base word is the adjective möjlig, which means "possible". By adding the suffix -het, it turns into the noun möjlighet (possibility or opportunity). A great rule to remember is that all nouns created with the -het suffix are en-words!

Why is it "den här möjligheten" with the definite "-en" ending? Doesn't "den här" already mean "this"?

Yes, den här means "this", but Swedish grammar requires the noun following it to also be in its definite form. It is literally like saying "this here the opportunity". Since möjlighet is an en-word (thanks to that -het ending!), its definite form becomes möjligheten.

Does "möjlighet" mean "possibility" or "opportunity"?

It means both! Swedish uses möjlighet for a "possibility" (something that could happen) as well as an "opportunity" (a chance to do something). The phrase ta möjligheten is the natural way to say "take the opportunity" in Swedish.

Why don't we use "att" before "ta" here?

Måste (must) is a modal verb. Just like in English, modal verbs are followed directly by the infinitive form of the main verb without using the infinitive marker att (to). So it is måste ta (must take), just as you wouldn't say "must to take" in English.