Debug/testing aids -- none of this is meant for players.
You wake up in a dark room, confused. Your body aches in a way that says you've been still for far longer than any one night's sleep. The air is cold and smells of dust. You don't recognize this place. You don't remember how you got here.
You now hold two runes. Tap Equip below and select both of them -- they'll fill one of the four boxes in your hotbar, in the bottom-right corner of the screen. Whichever box lights up is the one Cast will use.
That hotbar box now holds both runes together. Face something and tap Cast to bring them into effect. The sealed candle in this room hasn't been lit in a long time.
Concept and Operator aren't the whole expression -- there's a third kind of rune, a Modifier, that changes how the other two behave. You've just learned your first one. Open Equip and try slotting it in alongside what you already have.
Transfer needs to know where to draw from. Face something with a property to affect and tap Mark as Source -- it stays marked across rooms until you clear or replace it. Leave nothing marked and a Transfer draws from you instead.
Build the expression you'll cast with the Cast button -- equipping is choosing which runes are in reach, not a saved combo.