I'm confused I have a switch OLED running 18.1.0 how do I do this?

I simply can't afford the games I definitely could just emulate but I wanna play on the actual switch

I have an OLED model running 18.1.0 I'm struggling to know what needs to be done so any help doing it would be great.

Also curious if there would be a way to switch between legit and non legit

I'm sorry I've been looking around the sub for awhile today and I can't find anything properly useful, I am possibly just being stupid tho.