Skills are packaged instructions for specific kinds of work — drafting a status update in your team's format, reviewing a document against a checklist, or summarizing a spreadsheet. You don't write the instructions; you pick the skill and hand it your material. In this short demo, we break down the two ways skills run: User-invoked — you trigger them on purpose with a slash command (like your morning brief). You decide when to run them. Agent-invoked — Arc reaches for them automatically when it recognizes the work. Drop in a CSV, ask "what's in this?", and Arc applies the Summarize Data skill on its own. Same skills. Two ways in: you call it, or Arc does.