You're doing it the hard way!
Highlight the bit of the track you want to retain and then EITHER click the 'Trim' button (illustrated here:
https://tinyurl.com/s2sqr3s ) OR press Ctrl and T together. Job done!
As you're new to Audacity, I'll try to anticipate your next problem, which is that you won't find a 'Save' button to save the edited track that you've just created. It's 'Export' (from the 'File' menu) that you need to use.