Based on the product photos the cut is relaxed and true to size, with room for a sweater underneath. The inner drawstring lets you pull the waist in if you prefer a shaped silhouette.
It's water-resistant rather than waterproof: the smooth matte fabric sheds drizzle and light rain comfortably, but it isn't intended for heavy downpours.
The hidden drawstring at the waist is there for exactly that — cinch it a little and the jacket follows your shape without squeezing.
Machine wash cold on a gentle cycle and hang to dry. The fabric dries smooth on its own, so no ironing is needed.