I am so confused as to how to play this and have no idea what the hell's even going on. I'm just flipping cards and getting fucked
You start in the town where you can "buy items" or go to inn ("perform sex rest" option).
Basically you have two routes - sell your sex charges at item shop and buy powerful items there (need to visit dungeon at least once to see wares in detail it seems) or use sex charges at inn to train Roswitha's sensitivity and orgasmLP. Training those is very difficult in the dungeon.
The goal of game is to "go to the dungeon" and clear every stage.
To complete dungeon, you need to go through every stage of it (stage counter shown on screenshot). Two ways to advance stage counter - either draw every single card or use "Gate" card - one of event cards which looks like some huge black boar next to red lava lake (shown on screenshot too).
Some cards will be visible from start, others will be hidden (there are items/events to scout them). Every card is either event(red back), monster(blue back) or item(green back). At start you may want to manipulate deck with shuffle, pass(skips) and delete(deletes top card) to avoid monsters until you can handle them. Two ways of losing - going out of HP (def stat helps mitigate dge) or going out of orgasmLP. When your sensitivity bar progresses you get a chance to orgasm (proportional to bar completion) and you lose 1 orgasmLP for each orgasm.
I think being naked means monsters are less likely to dge HP and instead go for sexual attack (panties block intercourse for example).
You can return to town unless in fight at any time under normal circumstances, so abuse it if you want. Your dungeon progress will reset obviously.
Leveling stats is super grindy, just find/buy good items.