So confused - car seat & stroller but also a travel bassinet thing?

Va

Ok, FTM here & im so confused lol

My husband and I registered for a Chicco KeyFit 30Zip car seat & a jogger stroller that the Chicco can click into with an adaptor.

However, I keep seeing women post about a bassinet car seat thing (2nd pic. sorry, i don’t know what they’re called) vs. the car seat.

So my question is - is just the car seat on its own not enough?? Or does baby need the bassinet thing too? What’s the purpose of both if the car seat clicks into the stroller too?