Scratch Jr. is a great way to learn and develop coding skills, but unless you have a school Chromebook, it requires downloading an app on a tablet or Chromebook, or downloading a desktop version for a desktop computer--Mac or PC. On a school Chromebook, you do not log in to access the app. Instead, on the login page, look at the bottom left hand corner for the word "Apps" and click on it, which will bring up a menu, and Scratch Jr. should be listed at the top. If it isn't showing on this menu, try logging in and click on the Launcher to see if Scratch Jr. is listed among the apps there.
Click on the link above to go to the Scratch Jr. homepage where you will find links listed for downloading the app on various devices.
Click on the link above to download a desktop version of Scratch Jr. for a Mac or PC.