Something you definitely have to do...

No references needed here.

HTH

This is an idiom (an elliptical form of a sentence meaning: "You certainly should do that"). The suggested translation "Let's do it" assumes that the words pertain to the speaker and one or more others ("us"), something that is not at all clear from the (absence of) context. In my opinion, it tends to be more of an exhortation, something you say to someone else without including yourself.
Hope this helps!

Regards,
Ineke Hardy