When the RPM's get between 2.5 - 3.5 or so on the display; that's the sound and its time to press the clutch and shift up a gear.

• Down shifting is more nuance so until you're good and familiar with the sounds and associated speeds maybe just ease off gas, use brake, and/or put into neutral to stop or slow down. But essentially the process for down shifting is just the reverse as above.
• Just never attempt to adjust the gears without first pressing and holding down the clutch and, when shifting, ease off the clutch once in desired gear.
• Grinding the gears will eventually destroy the clutch, at which point your parent(s) may attempt to put you up for adoption or worse.