These icons are called SF Symbols. There are over 2,400 symbols you can use in iOS 13 and later, macOS 11 and later, watchOS 6 and later, and tvOS 13 and later. You can use a symbol everywhere you can use an image.

To browse the full set of symbols, download the SF Symbols app. For more info about SF Symbols check here.

SF Symbols 2 introduces over 750 new symbols and includes:

• Over 150 preconfigured, multicolor symbols that automatically adapt to vibrancy, accessibility settings, and appearance modes
• Negative side margins in both standard and custom symbols, giving yougreater control over horizontal alignment
• Localized symbol variants for right-to-left writing systems, as wellas script-specific symbols for Arabic, Devanagari, and Hebrew

Usage

UIKit:

let heartImage = UIImage(systemName: "heart.fill")

SwiftUI:

let heartImage = Image(systemName: "heart.fill")

The App by 

Apple has a dedicated App for this called SF Symbol. You should download the latest version from here to browse the full set of symbols.

Important Note

You should always stay with the app to have new symbols available for preview, export and enjoy.

Backward compatibility.

If you need to use new symbols like the new multi-color ones that introduced in SF Symbols 2.0 for iOS 14 and above, you can export them using the app itself and import them as assets in the project. Step 1 and 2 of this answer shows how you can export symbols to use it for older iOS versions

You can use SF Symbol Images in SwiftUI

Image(systemName: "person")

Download Link : https://developer.apple.com/design/resources/