Pack n' Play Question

We registered for a pack n' play and received it for our shower. The plan is to use it in our bedroom for baby to sleep in when he first comes home. I assumed the safest way for him to sleep would be on the mattress in the bassinet position (mattress is up higher and it is easier to reach baby). Here is my question: when/how did you utilize the portable napper if yours came with one? Is it safe to use for infants, or did you wait til your little one was a bit older? FTM and I want to make sure I'm using it properly. Thanks!