You can learn more about plugins by visiting Joplin Plugins.
For the ABC Sheet Music plugin, add "abc" after the first triple backtick like so: ```abc. If nothing happens, press Ctrl+L until sheet music shows right of your notation.
If the TimeTagger plugin doesn't work with TimeTagger running and plugin settings configured properly, note that here: Plugin: Time tracking with TimeTagger - Plugins - Joplin Forum.
Otherwise, you first need to self-host or sign up for TimeTagger, have it running, then configure plugin settings before trying to start the timer.