Granny House is a stealth-horror escape game: you're locked in an abandoned asylum with someone who hears everything, and the way out is a series of items and locks scattered through the building.
Noise is the whole mechanic. Running is fast and loud; walking is slow and safe. Every decision is a trade between the two, and the building is designed so that the fast route is usually the one that gets you caught.
Move quietly. Running is much faster but loud enough to bring her to you, so the safe play is walking by default and only sprinting once you've already been seen.
No — it's a stealth game. Hiding, quiet movement and knowing the layout are your only tools.
Yes — it runs in the browser with nothing to install. Use headphones.