To put aside all differences, all fears, all worries, and just go for it.
To make the most out of that part of time.
Roman Girl: i dunno...
Roman Boy: c'mon, carpe diem!
Roman Girl: okay!
Commonly used to justify spontaneous behavior and to make the most out of today, because one doesn't know if they'll live to see tomorrow.
However, the actual phrase is not saying to ignore the future, but rather to do as much as one can now because they won't know if everything will fall into place in the long run.
Benefit yourself now, so it can pay off in the future.
The complete fucking opposite of YOLO.