What does it mean when u don't have your period you only spot?

Depends: If you miss your period or only spot, you could be pregnant or you could have a lighter than normal period. I recommend getting a pregnancy test. If that is negative, then there are many many reasons for spotting. Much depends on your age, if you are on contraception, and many other factors.

Many conditions: If you are on contraception then itr is okay to have light cycles. Otherwise see your gyne.