Linux - zip unzip

$ ls readme
readme
$ zip readme

zip error: Nothing to do! (readme.zip)
$ ls readme*
readme
$ zip readme.zip readme
  adding: readme (deflated 4%)
$ ls readme*
readme  readme.zip

$ zip readme.zip aaa.txt bbb.txt 
  adding: aaa.txt (deflated 86%)
  adding: bbb.txt (deflated 82%)

 

zzh@ZZHPC:~/Downloads$ unzip rbay.zip -d rbay