how can i use 先……再 先……又

先，再 is for sequence
先A, 又B on top of A, did B

先 再means first second...
又means you did it over one time.
ur sentence 先吃了苹果，又吃了香蕉，means u did the action 吃 over one time.
我又看到他了。what's the meaning of it?
yes, it means u saw him the second time or the third time...
又 means u did the action, so we usually use 又 了 together