的
de
I s.p.
1) of subordination
我买的书 the book I bought
2) noun-forming, like English -er
看门的 doorkeeper
II cons.
(shì) A 的: action emphasizing A
我是昨天买的。 It was yesterday that I bought it.
我想(是)不会下雨的。 I think it's unlikely to rain.
III cons.
1) coll. by
这间屋子是五米的六米，合三十平方米。 This room is 5 x 6 meters, or 30 square meters.
2) topo. plus
五个的六个，一共十一个。 Five plus six is eleven.