It's the app with the icon that resembles a stack of blue, red, yellow, and green layers. It's the second tab at the top of the screen.  It may take a couple minutes for the engine to start. Type the email address and password associated with your Google account.  Type your first and last name, if they don't automatically populate, and click the left arrow. The search bar is located in the upper-left corner of the app.  It's next to the yellow image of an hourglass. It's the app with a black icon with a white music note in the center. The popup just tells you that the app needs to access your camera and other parts of your device. Once the app is installed, you can click "Open".  You can now sign in or create an account to start using TikTok your computer.  Whenever you want to use TikTok on your computer, just launch BlueStacks, click "My Apps" and then click TikTok .

Summary:
Open Bluestacks. Click App Center. Sign in to your Google account. Type Tik Tok in the search bar. Click the TikTok app. Click Accept in the popup. Click Open.