Transitioning baby car seat (FTM)

Justine ♡ • MAMA to a beautiful boy. ♡

I seen a post on FB about people switching car seats, & I was wondering

when do you do this & then how does that work when the car seat you have connects to the stroller you have ? Is it primarily just switching out the car seat to a new bigger extended back facing one then throwing out the original baby newborn seat?

Sorry if this is dumb haha