When to use it
Use it when you've been handed something new. You're honest that it's unfamiliar, and you set a realistic time to get comfortable with it. People mostly want to know you'll handle it, not that you already know everything.
Example
Manager: “Can you run the quarterly forecast this time?”
You: “This is new for me. I'll be up to speed by Friday. Is there a past version I can learn from?”
In an email or Slack message
In email: “Happy to take this on. It's new for me, so I'll spend this week getting up to speed and share a first draft Friday.” Pair the gap with a date.