ｆａｓｔ是动作快
ｓｏｏｎ是指在未来近期的时间内
ｆａｓｔｌｙ不是个字
”他很快就将学会咽下食物了“这句话里指的是婴儿在不久的时间之后（很快）就会学会自己嚼东西,而不是他吃东西会吃得很快.
再举几个例子参考一下：
He is a very fast runner.
That is a very fast car.
I came as fast as I could.
Julie will be getting married soon.
Soon,he will be a father.
Please let me know as soon as you can.