I just don't get byobu's keybindings systems, or?

Byobu's keybindings are guaranteed to work perfectly in Ubuntu with gnome-terminal.

Other terminals in Ubuntu, like Terminator, xterm, konsole, etc, should work fairly well, but might lack some features only found in gnome-terminal.

Other OSes (Windows, Mac), and with other terminals (iTerm2, Putty) are very difficult to support, and may or may not work well.

You can find a ~10 minute long "getting started" video at https://www.byobu.org/ which will walk you through the most common Byobu workflows and keybindings.

Also, you can press Shift-F1 any time in Byobu to bring up a screen of key binding hints. I'll copy and paste those here for you, in case Shift-F1 isn't working for you:

Byobu is a suite of enhancements to tmux, as a command line
tool providing live system status, dynamic window management,
and some convenient keybindings:

  F1                             * Used by X11 *
    Shift-F1                     Display this help
  F2                             Create a new window
    Shift-F2                     Create a horizontal split
    Ctrl-F2                      Create a vertical split
    Ctrl-Shift-F2                Create a new session
  F3/F4                          Move focus among windows
    Alt-Left/Right               Move focus among windows
    Alt-Up/Down                  Move focus among sessions
    Shift-Left/Right/Up/Down     Move focus among splits
    Shift-F3/F4                  Move focus among splits
    Ctrl-F3/F4                   Move a split
    Ctrl-Shift-F3/F4             Move a window
    Shift-Alt-Left/Right/Up/Down Resize a split
  F5                             Reload profile, refresh status
    Alt-F5                       Toggle UTF-8 support, refresh status
    Shift-F5                     Toggle through status lines
    Ctrl-F5                      Reconnect ssh/gpg/dbus sockets
    Ctrl-Shift-F5                Change status bar's color randomly
  F6                             Detach session and then logout
    Shift-F6                     Detach session and do not logout
    Alt-F6                       Detach all clients but yourself
    Ctrl-F6                      Kill split in focus
  F7                             Enter scrollback history
    Alt-PageUp/PageDown          Enter and move through scrollback
    Shift-F7                     Save history to $BYOBU_RUN_DIR/printscreen
  F8                             Rename the current window
    Ctrl-F8                      Rename the current session
    Shift-F8                     Toggle through split arrangements
    Alt-Shift-F8                 Restore a split-pane layout
    Ctrl-Shift-F8                Save the current split-pane layout
  F9                             Launch byobu-config window
    Ctrl-F9                      Enter command and run in all windows
    Shift-F9                     Enter command and run in all splits
    Alt-F9                       Toggle sending keyboard input to all splits
  F10                            * Used by X11 *
  F11                            * Used by X11 *
    Alt-F11                      Expand split to a full window
    Shift-F11                    Zoom into a split, zoom out of a split
    Ctrl-F11                     Join window into a vertical split
  F12                            Escape sequence
    Shift-F12                    Toggle on/off Byobu's keybindings
    Alt-F12                      Toggle on/off Byobu's mouse support
    Ctrl-Shift-F12               Mondrian squares
/usr/share/doc/byobu/help.tmux.txt (END)

Full disclosure: I am the author and maintainer of Byobu.