When something shrivels, it becomes smaller and wrinkled, usually because it is losing water or drying out.
When something shrivels, it is usually not good because it means it is getting old or damaged.
Examples:
The old apple shrivels in the sun.
The flower shrivels up without water.
The grape shrivels and becomes a raisin.
The balloon shrivels and becomes small and wrinkled.
My skin shrivels in the hot sun.
The plant shrivels and looks like a little old man.