What is Google Keep? A note-taking service available through Google, just like Docs, Slides, Gmail, etc... If you have a google account, you have a Google Keep account. You can find it in the waffle grid at the top right corner of your Google homepage on Chrome (see image.)
How can I add the Google Keep Chrome extension to help me take notes more easily? You can do it from the Chrome Web Store or directly from the Keep page, as well. It is free.
Once you install it, pin it so it is easier to access. When you want to take a note, just click on the Keep icon and start writing. If you are using it to take notes while watching a video in your browser, you can keep adding your notes as you go. (see image)