How to correctly use dispatch_sync, dispatch_async, dispatch_after and other GCD functions in Swift 3, 4 and newer?

Hello everyone! I'm transitioning from Objective-C to Swift, and I'm confused about Grand Central Dispatch (GCD) after the release of Swift 3. Previously I wrote something like: ```swift dispatch_async(dispatch_get_main_queue(), { // UI update }) ``` But now Xcode says this is incorrect. I understand that Apple changed the API, but I can't find a clear explanation of how to work with GCD in Swift 3, 4 and newer. I need to understand: 1. How to execute code asynchronously on the main queue (for UI updates)? 2. How to execute code synchronously (dispatch_sync) on a background queue? 3. How to add a delay before execution (dispatch_after)? 4. How to create my own queue? I tried writing like this, but it doesn't work: ```swift DispatchQueue.main.async { // code } DispatchQueue.globa