又 is used in declarative sentences and describes the simple repetition of actions. This repeated action has already occurred once in the past. 

S + 又 + Verb + 了 

电视机又出故障了。

The TV is acting up again.

他们又在挖路了。

They're digging up the road again. 

又 is sometimes used to express that something that has happened before is going to happen in the immediate future. In this case, it usually appears with 要、可以、能、是。 

S + 又 + 助动词/谓语动词 + Object 

这预示了又是个大冷天。

It promised to be another cold day. 

我想你又要像往常一样迟到了。

I guess you'll be late again as usual. 

再 is used to express something that has already happened and will happen again. 

S+ 再 + Verb 

他们再一次把垃圾拿出去了。

They took the garbage out again. 

我们明天再继续讨论。

Let's carry on this discussion tomorrow. 4

再 can also be used to express the equivalent of the English word 'another". 

S + 再 + Verb + Object 

我能再吃一个苹果吗？

Can I have another apple? 

再过几天 can be used with 先 to express sequential order. 

S + (行) + Action 1 + 再 + Action 2 i

先读说明再答题。

Read the instructions first and then answer the questions.