That means the invitation letter is the basic document I need to have.

也就是说我首先需要的是最基本的文件就是一封邀请函。

OK, I see. That means the invitation letter is the basic document I need to have. Then I will e-mail the organizer of this conference to provide me with an invitation letter.

我明白了，也就是说我首先需要的是最基本的文件就是一封邀请函。那么我会给这次会议的主办方发一封电子邮件，要求他们给我发一封邀请函。