@rooster gives a great answer.
And he also provides a terrific snippet for you to paste into your 100 Days Playground file. Create a new Playgrounds page, name it Dictionary Examples, and write some notes to FutureYou. FutureYou will thank you for thinking ahead. I hope, by now, you have a large collection of snippet pages in Playgrounds, all with appropriate names, allowing you to quickly search, and execute working code snippets.
But please note, another programmer @greenis is on Day 19 and is also asking a question about dictionaries.
See->Day 19 Dictionary Question
You're 20 days ahead of @greenis! To help you lock the lessons into the squishy SwiftUI portions of your brain, it might be time for you to start helping others on their journey. Take a moment to review help requests. Jump into Playgrounds and think of a creative solution. If you can explain the answer to yourself, and demonstrate it in code, you can explain it to other programmers.
But the real benefit is you are solidifying the vague concepts in your brain into bona-fide developer confidence!