Learn Swedish: Han spelar pianot mycket skickligt. - He plays the piano very skilfully.

Skickligt is an adverb here, which means it describes how he plays. In Swedish, you usually turn an adjective into an adverb by adding -t. Since the adjective for 'skilful' is skicklig, adding -t gives us skickligt ('skilfully').

Adding a -t is also how we make adjectives match 'ett' words. Is this the same thing?

The spelling rule is exactly the same, but their jobs in the sentence are different! If a word describes an ett noun (like ett skickligt barn - a skilful child), it is an adjective. Because it describes the verb spelar here, it acts as an adverb.

Why does the sentence use pianot (the piano) instead of just piano?

Just like in English, Swedish can use the definite form (adding -t to the ett word piano) when talking about playing the instrument. You will also frequently hear people drop the definite ending and just say spela piano when talking about the general skill.

I learned that mycket means 'a lot' or 'much'. Why is it translated as 'very' here?

Mycket does double duty in Swedish. When it describes a noun, it means 'much' or 'a lot' (like mycket vatten). But when you put it right before an adjective or an adverb like skickligt, it translates to 'very'.