1
I love watching the garden from the window.
I love looking at the garden from the window.
If you mean that you enjoy how the garden looks, use look at. Use watch when you follow something happening or changing over time: ‘I love watching the birds in the garden.’
2
When she went into the room, she watched that it was a mess.
When she went into the room, she saw that it was a mess.
Use see when you notice something with your eyes. Watch means looking at something for a while, often because it moves or changes.
Check our grammar lesson on the difference between look, watch and see.