The word 再 (zài) actually has a lot of uses, beyond just "again." "先..., 再..." (xiān..., zài...) is a pattern used for sequencing events, much like "First..., then..." in English. This pattern can also include "然后" (ránhòu) meaning "and after that."

General Usage of 先……再……
In the pattern below, 再 has a meaning of "then" or "and then."
Structure

Examples

Wǒ xǐhuɑn xiān xízǎo, zài shuì jiào。
我 喜欢 先 洗澡,再 睡觉。
I prefer to take a bath before I go to bed.

Using 再说
You may have learned that "再说" can mean "in addition." Well, this usage of 再 is a more literal combination of 再 + 说, fitting into the 先……再…… pattern.

So in this usage, 再说 doesn't really mean "in addition." Rather, it most literally means "and then we'll talk." In other words, "let's just do this now," and then after we see the result, we can talk some more about next steps. There's kind of a "let's see how this goes first" feeling to the expression.

Structure
Note that in the pattern below, the sentence normally ends with 再说.

Examples

Nǐ men xiān tǎo lùn yí xià zài shuō.
你们 先 讨论 一下 再说 。
You guys discuss a little first, then we'll talk.