If you've picked up a Chromebook (or Chromebox), you'll know you don't get very much in the way of local storage — the system is designed for the cloud after all. Still, there are times when saving files locally is a good idea (watching movies offline for example) and you want to manage those handful of gigabytes effectively. Here's how.
There are a couple of ways to see what's taking up the storage space on your Chromebook (you typically get 16GB of space to play around with, the same as a budget smartphone). Either launch the Files app and tap the menu button (three vertical dots) or type
chrome://quota-internals into a browser address bar and check that way.
You can see which sites are caching excessive amounts of data under the Usage & Quota tab of the Quota Internals page, but for a more user-friendly look at the situation, head to the Chrome OS Settings page, then click Stored data. Select any entry to see storage usage, permissions granted and even battery drain for the site in question. Tap Clear to erase the cached data.
The Files app can be used to delete local files as well of course, via the handy trash can icon on the toolbar. The old Windows shortcuts can prove helpful here: Shift and Ctrl to select multiple files at once, Ctrl+A to select everything in a particular folder, and then Alt+Backspace to delete.