The TTS feature is pretty nifty (on Android, not sure if there's an equivalent on the web version, though firefox reader mode has TTS). With bluetooth headphones/speaker I can just have a bunch of articles read to me while I'm doing something else.
[0]: I hate random buttons for services I don't use showing up in my browser unexpectedly! I think stuff like this is part of why so many people (at least used to) avoid automatic updates. UI changes that don't immediately benefit the user.
Select the pencil-like icon on the right of the top bar (hover over it to see words "Bulk Edit"). Select the articles you want to delete, then select the trashcan to delete them.
On the Kobo, you are limited to deleting one item at a time, unfortunately. So you bulk edit on the web, then sync your Kobo to remove the items.