Push the clutch. Downshift a gear. With the clutch still pushed in, rev the engine to roughly where it would be revving if it were in the “new” gear. Let go of the clutch pedal with the engine still revving.
No braking effect at all until you start letting go of the gas. Unless you want the clutch to last 30,000 miles, that’s the way a downshift should be done.
Double-clutching to save on synchros is optional (my first car has no synchro on 1st gear) 🙂