Learn Danish: Jeg kommer til at tabe glasset! - I am going to drop the glass!

In Danish, vil usually implies intention or desire. Since dropping a glass is an accident, using vil would sound like you want to drop it! We use kommer til at for things that will happen in the future unintentionally or inevitably.

I thought tabe meant 'to lose'. Why is it translated as 'to drop' here?

You are right that tabe means 'to lose' in many contexts, like losing a game or losing weight. However, when talking about a physical object slipping from your hands, tabe specifically means 'to drop'.

Why is 'the glass' written as glasset instead of det glas?

Danish normally attaches the definite article ('the') to the end of the noun. Because glas is an et word (et glas), it takes the ending -et to become glasset. You would generally only use det glas if you meant 'that glass' or if there was an adjective describing it.

What form of the verb follows kommer til at?

It is always followed by the infinitive form, which is the basic dictionary form of the verb. In this sentence, that is tabe. The word at ('to') right before it is your clear signal that an infinitive is coming!