Is this like "behöver", where you don't need an "att" before the infinitive?
Yes, it's possible to have an att before the infinitive here, but it looks better without it.
It means something like 'grab', 'catch', 'get hold of' – like, to take something with your hand.
It comes from latin poet Horatius Flaccus. Carpe diem, it means seize (catch) the moment because we dinnæ ken what we are going to be tomorrow, so enjoy the moment and your life. All the best for your Swedish pal ;-)
Carpe diem is a common theme in literature, expressing the shortness of life and the need to accomplish something enduring today. https://interestingliterature.com/2016/11/02/10-of-the-best-seize-the-day-poems-in-english/