How do flipsided cards work

I'm just curious how dual-sided cards that are not transform work. Cards such as hagra broodpit/Hagra Mauling and Witch-blessed Meadow/Witch enchanter.

They don't have a means of transforming like a normal double-sided card and I honestly never seen these before today. So do you just choose which one you want to play or is there a way to play one into the other? Some detailed explanations would be really helpful