r/learnelectronics

Stupid question (and idk if this is the right subreddit), but I'm trying to design a 5A tolerant DC Power supply pcb for 12V input and 5 and 3.3V outputs. My senior said I should try having 2 rails for each output voltage- Clean and dirty rails (to separate noisy loads from sensitive loads ) So I'm a bit lost on how to create this divide? I don't think a simple lc filter will suffice?
It's a 4 layer PCB, do I use 2 separate grounds for both the rails and then connect both the grounds to one common ground layer