AP Mode Vs Router Mode

Forgive a newbie’s confusion. I have Comcast for my ISP, a Netgear CM500 modem, and a Netgear Nighthawk X6 AC3200 router. It seems AP Mode is for when you have two or more routers, but the Netgear CM500 is just a modem. So am I okay to leave AP Mode off for the Nighthawk router? (Seems to work okay. I'm just worried about security and other problems.) Thanks!