Définition:
It’s not that big a deal, it’s not that difficult.
Exemple:
When someone complains about the impossibility of a task, the French expression ce n’est pas la mer à boire is the answer; you can use it to let that person know that whatever they have to do, it’s not as difficult as drinking the entire sea would be.
Par exemple…
Je dois tout refaire mais ce n’est pas la mer à boire.