Welcome to the forums, PierreF!
Take a look at our list of "Idioms & Slang" here. (You will find a useful list of idioms in the drop-down menu for "Members", which is located at the top of this page.)
Please note the typo in the first word of the meaning. The word "Of" should be "If".
In AmE the expression "swim or sink" has the same meaning as "sink or swim" but the preferred idiom is "sink or swim".
Student or Learner