what is difference using of "地" and "得"
There are three confusing words in Chinese: "的", "地", and "得".

For "的", it is usually used to describe the words following it. The structure is adj. + 的 + noun, for example, 勤劳的妈妈.

For "地", it is usually used to describe the action following it. The structure is adv. + 地 + verb, for example, 积极地回答问题. So 很快地吃 is correct. In a whole sentence, it might be 他正在很快地吃苹果.

For "得", it is usually used to describe the action before itself. The structure is verb + 得 + adv., for example, 回答得很好, or 吃得很快.