first, firstly, first of all & at first

1. firstly / first (of all) / in the first place / to start with / to begin with 常用于列举一系列原因、看法、评论及方式等。如： 

There are three reasons why I don’t like him: first(ly)/ to start with he’s rude, second(ly) he’s a liar, and third(ly) / finally he owes me money.

2. 人们用first (of all) [而不是firstly ]并且往往根据时间顺序依次列出一系列的动作。如：

First of all I get dressed, next I bring in the paper, then I fix breakfast.

3. at first只能用于表示一段时间，常与稍后的一段时间作比较。to start / begin with 和in the beginning 也可以这样用。如：

You’ll find it difficult at first / to begin with, but later / soon it’ll get easier.

4. 另外，first可以用来修饰动词。如：

  Who came first in the race?

 “Do you want a drink?” “I’ll finish my work first.”