if you use chrome browser:
Download the chromedriver.exe for selenium from https://chromedriver.chromium.org/downloads according to your chrome browser version and operating system then place it in the same directory as the main python file(yt-downloader.py)
if you use firefox browser:
Download the geckodriver.exe for selenium from https://github.com/mozilla/geckodriver/releases according to your operating system and then place it in the same directory as the main python file(yt-downloader.py)
--After downloading simply modily the line 25 of the code (change the filename to the driver that you just added to the project directory)i.e. path = os.getcwd() + "[name of the driver].exe"