You can upload a file with the 'Choose File' button. It will start playing immediately. Try downloading and uploading this video to get started.
If you want to pause it to take notes, you can hit the Annotate button. This will display the timestamp of when you paused it below the video.
You can then type your notes in the text box. Clicking 'Add note' will add the note to the list of Notes under the last pause timestamp.
To continue watching, just click 'Continue playing'. Feel free to use the 'Annotate' and 'Continue playing' buttons to keep pausing, taking notes and resuming the video.
When you're done, with the 'Save' button, you can download the notes as a .csv file, which can be opened by any spreadsheet software.