Outline:

    Install Audacity once through Synaptic Package Manager
    Listen to the original tutorial
    Time the begin time of each sentence
    Open Audacity
    Start narrating with appropriate pauses between sentences
    Record in one go
    Split the audio into sentences
    Starting from the back, slide the clips to match the noted timing
    When done, save the audio stream in ogg format
    Using ffmpeg commands, separate the video component from the original tutorial
    Using ffmpeg again, merge the dubbed audio and the seperated video component to create the dubbed tutorial