iTunes or Apple Music depends on the operating system you're using. Here's where you can find them:

On macOS:
macOS Catalina (10.15) and Later:

iTunes was replaced by Apple Music.
You can find Apple Music in your dock or by searching for it using Spotlight (press Command + Space and type "Music").
Open Finder to manage devices like iPhones or iPods connected via USB.
macOS Mojave (10.14) and Earlier:

iTunes is still available and located in the Applications folder.
You can also search for "iTunes" using Spotlight.
On Windows:
Download iTunes from:
The Microsoft Store (on Windows 10 or later).
Apple's official website if you're using an older Windows version.
Once installed, you can find iTunes in the Start Menu under "All Apps.