To install TurboTax in OS (operating system), first, ensure that your computer meets the system requirements specified by TurboTax. Then, visit the official TurboTax website and log in or create an account. Choose the version of TurboTax that suits your tax situation and follow the prompts to download the software. Once the download is complete, locate the installation file and double-click to run the installer. Follow the on-screen instructions to install TurboTax on your OS. After installation, launch the software, and you can start preparing and filing your taxes. Remember to keep your TurboTax account credentials secure for future access.