"flycat" got very good answer. but in the old time, people mixed them up sometimes.

“的” 一般修饰名词，放名词后。“地”则修饰动词，放副词后。 “的”is used for adjective,usually followed by a noun,for example" a big room"==" 一个大的房间”。 whereas,"地“ for adverb, by a verb, like " speak loudly"==”大声地说话“。 but nowadays, there's not big distinction between this two words, people sometimes use "的” for verbs and nouns.

‘的’用于形容词后，如： 美丽的花儿。 ‘地’用于副词后，限制动词。如：加速地奔跑。