If you want to save videos without installing an app, there are many websites where you can paste the URL of the YouTube video and then click on the resolution you want to download. Some even let you paste in a YouTube playlist and automatically download all the videos. Most apps allow you to build up a list of videos and then download them in one go.
Then you choose any options, such as the resolution to download, then hit the Download button.
The process is virtually identical to using a website: you copy and paste the URL of the video into the app.
