I'd like to make a map that users can pinpoint a city and add a tag to it. Is there anyway to do this?

Lots of ways to do things like this. The method will depend on your skill and ambition. At minimum you'll want to create some logic to load a custom class file when the callout bubble on a location is tapped. Maybe dig a bit into the docs and see Custom Plugin choice screens and see if you can get a Custom UIViewController to load when you tap the bubble. To make your custom UIViewController just copy a built in one in your project and rename it. Start there...if you can get your custom contorller running on taps then you can engineer the next steps to tag things, send data to your backend, etc. You'll need to get your head around making your own class files (usually copy / renamed from existing files) and then create a Custom Plugin screen using your new class file name.